Karthik/5438/deprecate horizon fields for protocol 22

[karthikiyer56]

Remove deprecated fields from horizon in protocol 22 release as a part of issue 5438 (https://github.com//issues/5438)

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've reviewed the changes in this PR and if I consider them worthwhile for being mentioned on release notes then I have updated the relevant CHANGELOG.md within the component folder structure. For example, if I changed horizon, then I updated (services/horizon/CHANGELOG.md. I add a new line item describing the change and reference to this PR. If I don't update a CHANGELOG, I acknowledge this PR's change may not be mentioned in future release notes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

• This PR removes 4 fields that have been deprecated, and were waiting for the next protocol release to be rolled out.
  They are numAccounts, amount, validBefore, validAfter from the AssetStat structure in services/horizon/protocols/main.go
• Additionally, the num_accounts and amount columns are also dropped from the exp_asset_stat tables and the DB bindings and code are removed

The PR that updates/removes the references for these deprecated fields from the stellar-docs is: stellar/stellar-docs#1014

[karthikiyer56]

As a part of this cleanup/deprecation task, I think the fields in Db structure ExpAssetStat also need to be removed.
I think that means the 2 rows in expat_asset_stat table need to be dropped.
can someone confirm if that is true?

horizon=# select   * from exp_asset_stats;
-[ RECORD 1 ]+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
asset_type   | 1
asset_code   | RFQP
asset_issuer | GDKFYFGSVF5F3JI32O5HPNXGVVQISKL5KYGOMW4V7IVNBERXA2EM4LBK
amount       | 0
num_accounts | 0
accounts     | {"authorized": 0, "unauthorized": 1, "liquidity_pools": 0, "claimable_balances": 0, "authorized_to_maintain_liabilities": 0}
balances     | {"authorized": "0", "unauthorized": "0", "liquidity_pools": "0", "claimable_balances": "0", "authorized_to_maintain_liabilities": "0"}
contract_id  |
-[ RECORD 2 ]+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
asset_type   | 1
asset_code   | MOON
asset_issuer | GDYIDXQRQLDKXDKOQ3RGWLUO2HMCQ2NTC35ZVG6QYOQY6XA5IGMI4IA6
amount       | 1000000000
num_accounts | 2
accounts     | {"authorized": 2, "unauthorized": 0, "liquidity_pools": 0, "claimable_balances": 0, "authorized_to_maintain_liabilities": 0}
balances     | {"authorized": "1000000000", "unauthorized": "0", "liquidity_pools": "0", "claimable_balances": "0", "authorized_to_maintain_liabilities": "0"}
contract_id  |
-[ RECORD 3 ]+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
asset_type   | 2
asset_code   | LQS1000008
asset_issuer | GAIRVTVFTAWHCJ3UOVXOVMLBJ2E325ZO5P6V5QPPPXVIANX6ATJMFILW
amount       | 10000000
num_accounts | 2
accounts     | {"authorized": 2, "unauthorized": 0, "liquidity_pools": 0, "claimable_balances": 0, "authorized_to_maintain_liabilities": 0}
balances     | {"authorized": "10000000", "unauthorized": "0", "liquidity_pools": "0", "claimable_balances": "0", "authorized_to_maintain_liabilities": "0"}
contract_id  |

[tamirms]

@karthikiyer56

As a part of this cleanup/deprecation task, I think the fields in Db structure ExpAssetStat also need to be removed.
I think that means the 2 rows in expat_asset_stat table need to be dropped.
can someone confirm if that is true?

Yes, you're correct. You will need to add a new migration which removes the amount and num_accounts columns from the exp_asset_stats table. Here is an example of a migration which does something similar that you can use as a reference point:

https://github.com/stellar/go/blob/master/services/horizon/internal/db2/schema/migrations/35_drop_participant_id.sql

[karthikiyer56]

@karthikiyer56

As a part of this cleanup/deprecation task, I think the fields in Db structure ExpAssetStat also need to be removed.
I think that means the 2 rows in expat_asset_stat table need to be dropped.
can someone confirm if that is true?

Yes, you're correct. You will need to add a new migration which removes the amount and num_accounts columns from the exp_asset_stats table. Here is an example of a migration which does something similar that you can use as a reference point:

https://github.com/stellar/go/blob/master/services/horizon/internal/db2/schema/migrations/35_drop_participant_id.sql

@tamirms
done