Bug 37787: Remove mention of elastic_index from POD

Bug 37787: Remove mention of elastic_index from POD

After the introduction of misc/workers/es_indexer_daemon.pl,
misc/workers/background_jobs_worker.pl should not handle the
elastic_index queue. But the latter script still mentions this
queue in the POD. This patch removes that mention.

To test:
- Run perldoc misc/workers/background_jobs_worker.pl
- Verify "elastic_index" is mentioned under --queue
- Apply this patch
- Run perldoc again and verify the mention of "elastic_index"
  is gone

Signed-off-by: Sukhmandeep Benipal <sukhmandeep.benipal@inLibro.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>