Remove deprecated Sidekiq rake tasks
What does this MR do?
This removes some Sidekiq rake tasks that weren't used any more. I marked these as deprecated in 12.7 (!22983 (merged)), and gitlab-com/gl-infra/scalability#255 (comment 314070862) points out that they predate Omnibus!
$ git describe 6a7d63aa47d583a21b87b623a010d8b98abb8777
v6.0.0-575-g6a7d63aa47d
For gitlab-com/gl-infra/scalability#255 (closed).