tests: Remove no longer needed /usr/bin/bash link

AFAICT the symlink we created in mbuto from /usr/bin/bash to /bin/sh was
for the benefit of a dhclient-script which used /usr/bin/bash as its
interpreter (e.g. in Fedora).  That was a bit risky if the script really
did require bash and we linked it to dash or another shell.

We now supply our own custom dhclient-script, so we don't need the
link any more.

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

test/passt.mbuto

@@ -19,8 +19,7 @@ KMODS="${KMODS:- virtio_net virtio_pci}"
 
 LINKS="${LINKS:-
 	 ash,dash,bash		/init
-	 ash,dash,bash		/bin/sh
-	 ash,dash,bash		/usr/bin/bash}"
+	 ash,dash,bash		/bin/sh}"
 
 DIRS="${DIRS} /tmp /sbin"