Ignore deprecated column and remove references to it
What does this MR do?
This is the first of 3 steps to removing
merge_requests_require_code_owner_approval from the database.
- Ignore the column in the class definition
- Drop the column from the DB
- Remove the ignoring of the column in the class definition
Data in this column has previously been migrated (!15862 (merged)) to individual ProtectedBranches records.
Originally, I wasn't aware of the 3-step process that is being used for this process, and thus was presented in a single MR: !18681 (closed)