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/issue_test.go

@@ -249,11 +249,11 @@ func TestIssue_InsertIssue(t *testing.T) {
 
 	// there are 5 issues and max index is 5 on repository 1, so this one should 6
 	issue := testInsertIssue(t, "my issue1", "special issue's comments?", 6)
-	_, err := db.GetEngine(db.DefaultContext).ID(issue.ID).Delete(new(issues_model.Issue))
+	_, err := db.DeleteByID[issues_model.Issue](db.DefaultContext, issue.ID)
 	assert.NoError(t, err)
 
 	issue = testInsertIssue(t, `my issue2, this is my son's love \n \r \ `, "special issue's '' comments?", 7)
-	_, err = db.GetEngine(db.DefaultContext).ID(issue.ID).Delete(new(issues_model.Issue))
+	_, err = db.DeleteByID[issues_model.Issue](db.DefaultContext, issue.ID)
 	assert.NoError(t, err)
 }