Re-remove the member_tasks table

What does this MR do and why?

Re-remove the member_tasks table

• no longer needed
• added with_lock_retries to mitigate issues from gitlab-com/gl-infra/production#16991 (comment 1607668540)

note: re-implementation of !134169 (merged) that was reverted via !134446 (merged)

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 #424804 (closed)