Implement hermit-unlink

hermit-unlink now deletes all symbolic links that connect to $HERMIT_PROFILE.. i think.
Okay, if you're trying to check the exit status of `readlink`, you don't need the square brackets, just put the call directly after the `if` and redirect it's output (both error and standard) to `/dev/null`.  The more appropriate way to test this is probably using the `-L` test of test.