_frontend/app.py: Remove unused import of `resource`

The `resource` import was unused.  Removed.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

buildstream/_frontend/app.py

@@ -20,7 +20,6 @@
 from contextlib import contextmanager
 import os
 import sys
-import resource
 import traceback
 import datetime
 from textwrap import TextWrapper