Delete any stale deploy access levels by group

What does this MR do?

With #14689 (closed) we fixed an issue where deploy access levels by group were not removed once the group is removed from the project. We left the deletion of such existing groups out of the security release in order not to complicate it (#14689 (comment 225478549)).

This MR adds a migration that will do the cleanup.

Execution plan for the DELETE query - https://explain.depesz.com/s/a1bY.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #33494