Remove deprecated release:merge task
What does this MR do and why?
We are cleaning up the old patch release code as we have moved to a new process.
This MR removes the release:merge
task as it is no longer needed with the new patch process.
The CherryPick::StableNotifier
and CherryPick::StableService
are also removed because this task was the only place they were used.
Related to gitlab-com/gl-infra/delivery#2755 (closed)
Author Check-list
- [-] Has documentation been updated?