fix #4003 (#4004)

Webhook and hook_task not cleaned up when delete repository

models/repo.go

@@ -1824,6 +1824,8 @@ func DeleteRepository(doer *User, uid, repoID int64) error {
 		&PullRequest{BaseRepoID: repoID},
 		&RepoUnit{RepoID: repoID},
 		&RepoRedirect{RedirectRepoID: repoID},
+		&Webhook{RepoID: repoID},
+		&HookTask{RepoID: repoID},
 	); err != nil {
 		return fmt.Errorf("deleteBeans: %v", err)
 	}