Remove redundant index_epic_issues_on_epic_id

Changelog: changed

db/post_migrate/20220204053655_remove_index_epic_issues_on_epic_id.rb

+# frozen_string_literal: true
+
+class RemoveIndexEpicIssuesOnEpicId < Gitlab::Database::Migration[1.0]
+  INDEX = 'index_epic_issues_on_epic_id'
+
+  disable_ddl_transaction!
+
+  def up
+    remove_concurrent_index_by_name :epic_issues, name: INDEX
+  end
+
+  def down
+    add_concurrent_index :epic_issues, :epic_id, name: INDEX
+  end
+end

db/schema_migrations/20220204053655

+d6b7fa6e5be83aa67bb479604bf6ddb9d8caae82fc8ea1ab7f34d5c534174ecf
\ No newline at end of file

db/structure.sql

@@ -26241,8 +26241,6 @@ CREATE UNIQUE INDEX index_epic_board_list_preferences_on_user_and_list ON boards
 
 CREATE UNIQUE INDEX index_epic_board_recent_visits_on_user_group_and_board ON boards_epic_board_recent_visits USING btree (user_id, group_id, epic_board_id);
 
-CREATE INDEX index_epic_issues_on_epic_id ON epic_issues USING btree (epic_id);
-
 CREATE INDEX index_epic_issues_on_epic_id_and_issue_id ON epic_issues USING btree (epic_id, issue_id);
 
 CREATE UNIQUE INDEX index_epic_issues_on_issue_id ON epic_issues USING btree (issue_id);