Add a CleanSpec for grep/toolbox.

I moved grep out of toolbox a couple of months ago, so hopefully no one
else should see this. Just in case, though, remove grep and toolbox so
they both get rebuilt and any symbolic links will find themselves pointing
to the right binary.

Bug: 19878755
Change-Id: I15f63500cae3578a82a895f851c797fd324bbe02