Remove unused database table column (moddb.Users.parent_user_id)

[jtpalmer]

Description

Adds migration to remove the parent_user_id column from the Users table in the moddb database.

Also bumps version numbers and adds migration boilerplate. This could be moved to a separate PR, but is needed for testing purposes.

Motivation and Context

This column is not used and causes problems with MySQL's strict sql_modes since it is NOT NULL and does not have a default value and no value was being set.

Tests performed

Manually tested migration:

• Installed Open XDMoD 6.5.0
• Upgraded to a build of this branch
• Ran xdmod-upgrade
• Observed that the column was removed

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.