removed PHP 5.3-ness from `mp6_colors_get_json()`

git-svn-id: https://plugins.svn.wordpress.org/mp6/trunk@760656 b8457f37-d9ea-0310-8a92-e5e31aec5664
removed `colors-blue.css`

git-svn-id: https://plugins.svn.wordpress.org/mp6/trunk@760657 b8457f37-d9ea-0310-8a92-e5e31aec5664