fix(mysql,mariadb): remove extra FROM from showIndexes

[ephys]

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Description Of Change

Our implementation of MySQL schemas is very broken. MySQL does not have a concept of 'database', and when you see the word 'database' in the MySQL doc, it actually means what we understand as 'schema' in our codebase (CREATE DATABASE and CREATE SCHEMA are synonymous in MySQL).

This PR also fixes our MySQL implementation of showIndexesQuery.

The query is defined as follows:

SHOW INDEX
  {FROM} tbl_name
  [{FROM} db_name]

Our implementation would generate this:

SHOW INDEX FROM `schema`.`tableName` FROM `databaseName`

Where databaseName is the name of the database from the connection credentials. The problem is that in MySQL, that is actually equivalent to doing this:

SHOW INDEX FROM `databaseName`.`tableName`

Which breaks because there is no schema called databaseName.

This PR fixes this by just removing the FROM `databaseName` part. The schema is already handled by our quoteTable function.

[github-actions]

🎉 This PR is included in version 7.0.0-alpha.15 🎉

The release is available on:

• npm package (@release-v7 dist-tag)
• GitHub release

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