Remove temporary index for migration

What does this MR do and why?

Remove temporary index for migration

Add migrations to remove indexes that were created to support a migration deleting from:

• protected_branch_merge_access_levels
• protected_branch_push_access_levels
• protected_tag_create_access_levels

Removing these indexes:

• tmp_idx_protected_branch_merge_access_levels_on_id_with_group
• tmp_idx_protected_branch_push_access_levels_on_id_with_group
• tmp_idx_protected_tag_create_access_levels_on_id_with_group

Contributes to: #430843 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #430843 (closed)