There were separate `freebsd`, `linux`, `cleanlinux`
and `cleanfreebsd` targets. But these just did the
same thing, so simplify them to just have an `all`
and a `clean` target: this means we have less to plumb
through from the top-level Magicka GNUmakefile.
Signed-off-by: Dan Cross <patchdev@fat-dragon.org>