Geo - Disable built-in Sidekiq retry for verification workers

From https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8550#note_121203478:

I'm not seeing where we disabled built-in Sidekiq retries. Are we currently double retrying failed verifications?

While we verify a repository on both primary/secondary nodes, we handle the possible errors that can happen and mark the verification as failed. Projects, where the verification has failed, will be picked again by the scheduler at the next time it runs. So, the built-in Sidekiq retry is not necessary for these workers.

/cc @mkozono @rnienaber