Cleans up tests/

We're making a lot of old tests that we don't need, and they all
bloat the size of the initramfs.  This cuts it from 48MB to 26MB or so,
for me.  Glibc still takes up 13MB.

Part of the reason each test is large (200KB+) is that they all
statically link parlib.

All of the tests still live in an old/ directory.  Feel free to add more
tests, in general.  Anything we'll regularly use can be in the main
tests/ directory.  I'm just tired of building (and copying across the
network) huge kernel images.

You might need to make userclean.

You'll also want to clean out binaries from kern/kfs/bin, since those
won't get automatically cleaned.  To do this, I mv'd busybox out of KFS
temporarily, then did:

$ find kern/kfs/bin -type f -exec rm '{}' \+

(or something similar) to remove the binaries, but not the symlinks for
busybox.  Then I mv'd busybox back.