Improve group and dashboard issuables query

What does this MR do and why?

Attempt removal of old query optimization because after testing a few queries, it seems to be faster without it.

Group issues

I'm testing this as a non-member which means it has the extra confidential clause. We skip this if the current user is Developer+ on the group.

Query	Before	After
gitlab-org no filter	hits: 657947 (~5.00 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63771	hits: 342830 (~2.60 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63770
gitlab-com no filter	hits: 717602 (~5.50 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63772	hits: 506291 (~3.90 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63773
gitlab-com label=None	hits: 862161 (~6.60 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63774	hits: 799005 (~6.10 GiB) https://postgres.ai/console/gitlab/gitlab-production-tunnel-pg12/sessions/19306/commands/63775
gitlab-com search=some search term

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