Remove Giant from linux_getcwd() due to VFS is MPSAFE now.

Discussed with:	kib
MFC after:	1 week

sys/compat/linux/linux_getcwd.c

@@ -450,11 +450,8 @@ linux_getcwd(struct thread *td, struct linux_getcwd_args *args)
 		 * limit it to N/2 vnodes for an N byte buffer.
 		 */
 
-		mtx_lock(&Giant);
 		error = linux_getcwd_common (td->td_proc->p_fd->fd_cdir, NULL,
 		    &bp, path, len/2, GETCWD_CHECK_ACCESS, td);
-		mtx_unlock(&Giant);
-
 		if (error)
 			goto out;
 		lenused = bend - bp;