Rename InstanceStatistics workers as UsageTrend workers

Eliminate the old, renamed workers from Gitlab and omnibus:

• analytics_instance_statistics_count_job_trigger_worker
• analytics_usage_trends_count_job_trigger_worker

The following discussion from !54153 (merged) should be addressed:

• @pshutsin started a discussion: (+4 comments)

  I think we need backwards compatibility here too since there can be jobs scheduled with old name. I think we should keep old class name available until next major release. https://docs.gitlab.com/ee/development/sidekiq_style_guide.html#removing-workers