Refactor deletion (#28610)

Introduce the new generic deletion methods
- `func DeleteByID[T any](ctx context.Context, id int64) (int64, error)`
- `func DeleteByIDs[T any](ctx context.Context, ids ...int64) error`
- `func Delete[T any](ctx context.Context, opts FindOptions) (int64,
error)`

So, we no longer need any specific deletion method and can just use
the generic ones instead.

Replacement of #28450

Closes #28450

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/issues/label.go

@@ -256,7 +256,7 @@ func DeleteLabel(ctx context.Context, id, labelID int64) error {
 		return nil
 	}
 
-	if _, err = sess.ID(labelID).Delete(new(Label)); err != nil {
+	if _, err = db.DeleteByID[Label](ctx, labelID); err != nil {
 		return err
 	} else if _, err = sess.
 		Where("label_id = ?", labelID).