Simplify calls to HTMLMediaElement::createMediaControls()

All calls to the above method is currently guarded by a check of the
predicate hasMediaControls(). The first thing createMediaControls() does
though is to check the same predicate.
Remove the checks at the callsites and leave the checking to
createMediaControls().

Review URL: https://codereview.chromium.org/539003003

git-svn-id: svn://svn.chromium.org/blink/trunk@181403 bbb929c8-8fbe-4397-9dbb-9b2b20218538