Remove HTMLMediaElement::updateActiveTextTrackCues log statement.

Remove an annoying log statement that prints all the time during the
lifetime of the HTMLMediaElement, but doesn't provide any value 99.999%
of the time.

Review URL: https://codereview.chromium.org/139753002

git-svn-id: svn://svn.chromium.org/blink/trunk@165166 bbb929c8-8fbe-4397-9dbb-9b2b20218538