Remove seemingly unneeded unlock/relock of the dvp in msdosfs_rmdir,

causing LOR.

Reported and tested by:	pho
MFC after:	3 weeks

sys/fs/msdosfs/msdosfs_vnops.c

@@ -1468,14 +1468,12 @@ msdosfs_rmdir(ap)
 	 * the name cache.
 	 */
 	cache_purge(dvp);
-	VOP_UNLOCK(dvp, 0);
 	/*
 	 * Truncate the directory that is being deleted.
 	 */
 	error = detrunc(ip, (u_long)0, IO_SYNC, cnp->cn_cred, td);
 	cache_purge(vp);
 
-	vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
 out:
 	return (error);
 }