Bug 1506759: remove try-except block which swallows OSError r=ted

We have a few bugs filed as intermittent failures all relating
to an `AssertionError` on the return value of this block, which
seems to have a relevant value when `OSError` is thrown. Removing
this will not fix the problem but will at least let us see the
true cause of the failure for debugging and stabilization.

Differential Revision: https://phabricator.services.mozilla.com/D11884

--HG--
extra : moz-landing-system : lando

python/mach/mach/test/test_telemetry.py

@@ -38,10 +38,7 @@ def run(*args, **kwargs):
                                 **kwargs)
         # Load any telemetry data that was written
         path = unicode(tmpdir.join('telemetry', 'outgoing'))
-        try:
-            return [json.load(open(os.path.join(path, f), 'rb')) for f in os.listdir(path)]
-        except OSError:
-            return []
+        return [json.load(open(os.path.join(path, f), 'rb')) for f in os.listdir(path)]
     return run