Mac h264: Remove CFRetainCount assertion

The CVPixelBuffers have an arbitrarily long lifetime now (they are
to be handed to an AVSampleBufferDisplayLayer). It will not guaranteed
that they are will be released by this call.

BUG=600685

Review URL: https://codereview.chromium.org/1881783002

Cr-Commit-Position: refs/heads/master@{#386572}
1 file changed