Drop old temporary vulnerability management indices

What does this MR do and why?

The migrations using these indices have all been finished.

Index	Introduced by	Introduced milestone	Finalized By
tmp_index_for_owasp_null_on_vulnerability_reads	!161962 (merged)	%17.4	This MR
tmp_idx_for_feedback_comment_processing	!104999 (merged)	%15.7	Too old to matter
tmp_idx_for_vulnerability_feedback_migration	!104599 (merged)	%15.7	Too old to matter
tmp_index_for_succeeded_security_scans	!144456 (merged)	%16.10	!147426 (merged)
tmp_index_on_vulnerabilities_non_dismissed	cbea6458	?	Too old to matter
tmp_index_vulnerability_overlong_title_html	!103218 (merged)	%15.8	Too old to matter

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