Cleanup unused tagging records

These are no longer used because we moved to a dedicated labels table a
very long time ago.

Changelog: other

db/post_migrate/20211028100303_tmp_index_for_delete_issue_merge_request_taggings_records.rb

+# frozen_string_literal: true
+
+class TmpIndexForDeleteIssueMergeRequestTaggingsRecords < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'tmp_index_taggings_on_id_where_taggable_type_issue_mr'
+  INDEX_CONDITION = "taggable_type IN ('Issue', 'MergeRequest')"
+
+  def up
+    add_concurrent_index :taggings, :id, where: INDEX_CONDITION, name: INDEX_NAME # rubocop:disable Migration/PreventIndexCreation
+  end
+
+  def down
+    remove_concurrent_index_by_name :taggings, INDEX_NAME
+  end
+end

db/post_migrate/20211028100843_delete_issue_merge_request_taggings_records.rb

+# frozen_string_literal: true
+
+class DeleteIssueMergeRequestTaggingsRecords < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = 'tmp_index_taggings_on_id_where_taggable_type_issue_mr'
+
+  BATCH_SIZE = 3_000
+  TAGGABLE_TYPES = %w(Issue MergeRequest)
+
+  def up
+    sleep 2 while ActsAsTaggableOn::Tagging.where(taggable_type: TAGGABLE_TYPES).limit(BATCH_SIZE).delete_all > 0
+
+    remove_concurrent_index_by_name :taggings, INDEX_NAME
+  end
+
+  def down
+  end
+end

db/schema_migrations/20211028100303

+bb28267d020cbc26614e4635c803af0168ab5606f3aadc40e1c0e0bc6d988254
\ No newline at end of file

db/schema_migrations/20211028100843

+27578f62b5cde4fdbfe79eb717404a5cef62b8c17170525428dbf81e6b394ce9
\ No newline at end of file