Staging: zcache: delete it

Dan Magenheimer says that it is now safe to delete zcache, so quick,
before he changes his mind, drop the thing on the floor and run
screaming away.

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>