Do not delete unblinded tokens

[NejcZdovc]

Right now we delete unblinded tokens when they are used. To have history we should just marked them as claimed. We need to add new column redeemed_at which should be timestamp and we insert time stamp when token is used. We also need to update query for getting all tokens as we need to return only tokens that don't have redeemed_at column populated.

[GeetaSarvadnya]

@NejcZdovc need a small clarification reg brave/brave-core#5017. Description of the issue says spent_at should it be redeemed_at? Also, I have sent tip of 1BAT to verified pubs in staging env. I could see records of 4 rows, what does each row indicate?

[NejcZdovc]

@GeetaSarvadnya updated issue. 1 BAT = 4 tokens (1 token = 0.25 BAT)

[GeetaSarvadnya]

Verification passed on

Brave | 1.10.79 Chromium: 81.0.4044.138 (Official Build) dev (64-bit)
-- | --
Revision | 8c6c7ba89cc9453625af54f11fd83179e23450fa-refs/branch-heads/4044@{#999}
OS | Windows 10 OS Version 1803 (Build 17134.1006)

• Verified the test plan from Adds redeemed_at to unblinded tokens, removes delete brave-core#5017
  

Verification passed on

Brave	1.10.79 Chromium: 81.0.4044.138 (Official Build) dev (64-bit)
Revision	8c6c7ba89cc9453625af54f11fd83179e23450fa-refs/branch-heads/4044@{#999}
OS	Ubuntu 18.04 LTS

• Verified the test plan from Adds redeemed_at to unblinded tokens, removes delete brave-core#5017
  

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Brave | 1.10.80 Chromium: 81.0.4044.138 (Official Build) dev (64-bit)
-- | --
Revision | 8c6c7ba89cc9453625af54f11fd83179e23450fa-refs/branch-heads/4044@{#999}
OS | macOS Version 10.14.6 (Build 18G3020)

• Verified test plan from

• Confirmed when promotion = UGP grant (staging env)

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