Fix broken XHProf unit tests

Summary:
There are two broken tests. One (007) is easy to fix. It was failing because of array-to-string conversion warnings.

Since I didn't want to add function calls because that would change the test output, I just silenced the warnings with "@".

The other test (004) was also easy to fix but I can't really explain what's going on there. Seems like it works though? It shouldn't do anything bad, since we would have generated a meaningless "???_op" otherwise.

Test Plan: Ran tests, tests passed.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10376