Remove build hooks worker and associated code

What does this MR do and why?

Remove the app/workers/build_hooks_worker.rb file and all uses of it.

All usages of the BuildHooksWorker were removed in 15.3 in this MR: !93665 (diffs)

See #371379 (closed)

MR acceptance checklist

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

How to set up and validate locally

This should not cause any changes, the hook has been redundant for a long time.

Related to #371379 (closed)