Remove temp index on approval_merge_request_rules

What does this MR do and why?

Addresses #372224 (closed)

Removes the temporary index created as part of !96293 (merged)

Migration Output

main: == 20221019102426 RemoveTmpIndexApprovalMergeRequestRulesOnReportType: migrating 
main: -- transaction_open?()
main:    -> 0.0000s
main: -- indexes(:approval_merge_request_rules)
main:    -> 0.0114s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0006s
main: -- remove_index(:approval_merge_request_rules, {:algorithm=>:concurrently, :name=>"tmp_index_approval_merge_request_rules_on_report_type_equal_one"})
main:    -> 0.0016s
main: -- execute("RESET statement_timeout")
main:    -> 0.0070s
main: == 20221019102426 RemoveTmpIndexApprovalMergeRequestRulesOnReportType: migrated (0.0292s) 



main: == 20221019102426 RemoveTmpIndexApprovalMergeRequestRulesOnReportType: reverting 
main: -- transaction_open?()
main:    -> 0.0000s
main: -- index_exists?(:approval_merge_request_rules, [:id, :report_type], {:name=>"tmp_index_approval_merge_request_rules_on_report_type_equal_one", :where=>"report_type = 1", :algorithm=>:concurrently})
main:    -> 0.0106s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0005s
main: -- add_index(:approval_merge_request_rules, [:id, :report_type], {:name=>"tmp_index_approval_merge_request_rules_on_report_type_equal_one", :where=>"report_type = 1", :algorithm=>:concurrently})
main:    -> 0.0044s
main: -- execute("RESET statement_timeout")
main:    -> 0.0005s
main: == 20221019102426 RemoveTmpIndexApprovalMergeRequestRulesOnReportType: reverted (0.0252s) 

MR acceptance checklist

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