Remove text output from media-document-audio-repaint

The repainting in this test is correct in all cases, but due to timing
issues the actual repaint rects are not consistent from run to run or
across platforms.

Therefore, remove any text output for repaint rects and leave this as
just a pixel test.

BUG=353934,345027

Review URL: https://codereview.chromium.org/204873002

git-svn-id: svn://svn.chromium.org/blink/trunk@169576 bbb929c8-8fbe-4397-9dbb-9b2b20218538