Remove temporary index added by vulnerability resolution migration

Proposal

A temporary index called tmp_index_vulnerability_reads_where_state_is_detected was added to the vulnerability_reads table by Add tmp index on vulnerability_reads for bbm (!161296 - merged) • Adam Cohen • 17.3 as part of Create data migration to automatically resolve ... (#444926 - closed) • Adam Cohen • 17.4 • Needs attention. The purpose of this issue is to remove this index once the batched background migration has been completed.