Drop TxMeta column from TxHistory table

[SirTyson]

Description

Rebased on #4226.

This change drops txmeta from the txhistory SQL table when BucketListDB is enabled.

Unfortunately, SQLite does not support conditional column deletion, so I've added a new persistent state field indicating whether or not txmeta is supported. This allows us to check if the txmeta column exists before executing the drop SQL transaction.

Addresses #4211.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[graydon]

I believe you can reflect on the table structure directly and check to see if it has a given column. For example in sqlite it's something like this:

SELECT EXISTS (
  SELECT 1
  FROM pragma_table_info('txhistory')
  WHERE name = 'txmeta'
);

and for postgres I think it's something like this:

SELECT EXISTS (
  SELECT 1
  FROM information_schema.columns 
  WHERE 
    table_name = 'txhistory' AND 
    column_name = 'txmeta'
);

[SirTyson]

I believe you can reflect on the table structure directly and check to see if it has a given column. For example in sqlite it's something like this:

SELECT EXISTS (
  SELECT 1
  FROM pragma_table_info('txhistory')
  WHERE name = 'txmeta'
);

and for postgres I think it's something like this:

SELECT EXISTS (
  SELECT 1
  FROM information_schema.columns 
  WHERE 
    table_name = 'txhistory' AND 
    column_name = 'txmeta'
);

Done

[MonsieurNicolas]

I think you need to make this schema change in the same place than other schema changes so that people can run the upgrade-db (some people don't give the account that runs core sql access to update schema)

[SirTyson]

Done

[marta-lokhova]

lgtm!

[marta-lokhova]

r+ 31dabd1