Remove GetHeight from ClientMessage interface

[colin-axner]

Summary

Following implementation of #284, #285, and #286, GetHeight will no longer be necessary. This removal is necessary for the Wasm Light Client

Remove GetHeight from the Header ClientMessage interface. Usage in 07-tendermint can use the casted header function (cast to 07-tendermint type and use the concrete function)

Should be done after no longer setting the consensus state in updates in 02-client

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[crodriguezvega]

Relayer operators might need consensusHeight (see comment).

[damiannolan]

Updated issue to reflect new interface naming 👍

[damiannolan]

After the discussion in #1208 linked above, the proposed solution moving forward is as follows:

• Remove the GetHeight interface method from ClientMessage.
• Return a list of heights []exported.Height from the new UpdateState interface.
• Maintain the consensus_height event emitted from 02-client client update handler, but mark as deprecated for future removal. For example, with tendermint lightclients this will simply be heights[0] following a successful update.
• Add an additional consensus_heights event, containing a list of updated heights. This provides flexibility for emitting multiple consensus heights from batched header updates.

[colin-axner]

closed! Great work @damiannolan