Remove redundant index_events_on_target_type_and_target_id

Changelog: added

db/post_migrate/20211104044453_remove_redundant_events_index.rb

+# frozen_string_literal: true
+
+class RemoveRedundantEventsIndex < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index_by_name :events, :index_events_on_target_type_and_target_id
+  end
+
+  def down
+    add_concurrent_index :events, [:target_type, :target_id], name: :index_events_on_target_type_and_target_id
+  end
+end

db/schema_migrations/20211104044453

+fc5a60c27ca89b122d798abe8f55a0951fece712c885555df0d2f37b565d6f94
\ No newline at end of file

db/structure.sql

@@ -25359,8 +25359,6 @@ CREATE INDEX index_events_on_project_id_and_id ON events USING btree (project_id
 
 CREATE INDEX index_events_on_project_id_and_id_desc_on_merged_action ON events USING btree (project_id, id DESC) WHERE (action = 7);
 
-CREATE INDEX index_events_on_target_type_and_target_id ON events USING btree (target_type, target_id);
-
 CREATE UNIQUE INDEX index_events_on_target_type_and_target_id_and_fingerprint ON events USING btree (target_type, target_id, fingerprint);
 
 CREATE INDEX index_evidences_on_release_id ON evidences USING btree (release_id);