Remove spurious DisableCompositingQueryAsserts in Internals.cpp

There's no reason to have an ASSERT disabler in this function. It looks like it
was added by mistake in https://codereview.chromium.org/138753006.

Review URL: https://codereview.chromium.org/373993002

git-svn-id: svn://svn.chromium.org/blink/trunk@177623 bbb929c8-8fbe-4397-9dbb-9b2b20218538