Remove unfinished file with the wrong name

doc/operations/sidekiq_restarter.md

-# Sidekiq MemoryKiller
-
-The GitLab Rails application code suffers from memory leaks. For web requests
-this problem is made manageable using
-[unicorn-worker-killer](https://github.com/kzk/unicorn-worker-killer) which
-restarts Unicorn worker processes in between requests when needed. The Sidekiq
-MemoryKiller applies the same approach to the Sidekiq processes used by GitLab
-to process background jobs.
-
-