Remove the media query expressions serialization cache

It is not needed as the expressions are not individually
accessible from CSSOM, and I suppose the cache only existed
as the serialization was done twice during creating of the
MediaQuery object. That is not needed as you can compare
the MediaQueryExp directly.

Review URL:

git-svn-id: svn:// bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed