pkg sql: handle setting "schema_locked" using the declarative schema changer

[shghasemi]

[blathers-crl[bot]]

Your pull request contains more than 1000 changes. It is strongly encouraged to split big PRs into smaller chunks.

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[cockroach-teamcity]

This change is 

[rafiss]

This is no longer needed, since it was handled in PR https://github.com/cockroachdb/cockroach/pull/158390