Allow MIME types without codecs to be passed to Chromium MediaSource code.

The Chromium code is in a better position to determine whether MIME types
w/o the codecs parameter should be supported or not. This change just removes
the checks in Blink that prevent these MIME types from reaching the Chromium
code.

BUG=280550
TEST=http/tests/media/media-source/mediasource-is-type-supported.html

Review URL: https://chromiumcodereview.appspot.com/23717002

git-svn-id: svn://svn.chromium.org/blink/trunk@156895 bbb929c8-8fbe-4397-9dbb-9b2b20218538