mq: fix failing qrefresh test

Additions to test-mq-qrefresh.t in f08df4d38442 (mq: ignore subrepos
(issue2499)) were originally based on a version prior to d0e21c5fde41
(subrepo: handle missing subrepo spec file as removed). This fixes a
test failure that resulted from the former being applied after the
latter, noticed by abuehl.

tests/test-mq-qrefresh.t

@@ -550,9 +550,7 b' test when deleting'
   $ hg qrefresh
   warning: not removing .hgsub
   warning: not removing .hgsubstate
-  refresh interrupted while patch was popped! (revert --all, qpush to recover)
-  abort: No such file or directory: $TESTTMP/repo-2499/.hgsub
-  [255]
+  warning: subrepo spec file .hgsub not found
   $ hg status
   ! .hgsub
   ! .hgsubstate