Synchronously add vulnerabilities_reads indexes

What does this MR do and why?

In a previous MR we added the two indexes asynchronously.

We need to add the indexes synchronously to complete the async index addition process outlined in the docs:

• Create indexes asynchronously

The indexes we added are copies of two existing indexes, with just the new has_vulnerability_resolution column appended. Therefore, we can also remove those now redundant indexes.

• The redundant indexes
  • index_vulnerability_reads_common_attrs_and_detection_for_groups
  • index_vulnerability_reads_common_finder_query_2

There was also a copy/paste issue with the down method in the async migration that I corrected.

MR acceptance checklist

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Verification that async migration is complete

Before async migration	After async migration

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Changelog: changed
Resolves: #493285 (closed)
Epic: &15036 (closed)