Remove lease from Event#reset_project_activity

What does this MR do?

This removes the exclusive lease used by Event#reset_project_activity in favour of conditional UPDATE queries. See dbcc623a for more information.

Why was this MR needed?

Obtaining the lease can, for whatever reason, be really slow. See for more information.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Merge request reports