Fix media type handling for CSS that's not loaded with only=styles

Fix media type handling for CSS that's not loaded with only=styles

We were only doing server-side @media wrapping in only=styles mode but
not in regular mode. Meanwhile, the client-side loader had dropped all
support for media types under the assumption that this was all handled
server side, which caused media type handling to break for modules
loaded the normal way. We didn't notice this before because the only
core module that uses this is skins.vector, which is loaded through
only=styles.

Change-Id: I8228cc0317328440256b45b166eef1b57dbf4602