Makefile: Remove unused test targets

The Makefile provides for "fast" and "full" variants of make check.
However, nothing seems to use or implement the "full" variant at all.
Further, the %.check and %.fastcheck targets are not actually used, with
other targets instead using the actual .ok tag file as the target.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>