Remove all minified assets from trunk.

This commit is part of a series that will re-organise BuddyPress trunk
to use a Grunt build process.

Minified CSS/JS will now only be created when a release build is
produced.
See #5160

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8372 cdf35c40-ae34-48e0-9cc9-0c9da1808c22