Remove stale comment about socket buffer accounting from access(2) code.

It is the case, however, that the uidinfo of the temporary credential
set up for access(2) is not properly updated when its effective uid is
changed.

MFC after:	3 days

sys/kern/vfs_syscalls.c

@@ -2122,8 +2122,7 @@ kern_accessat(struct thread *td, int fd, char *path, enum uio_seg pathseg,
 
 	/*
 	 * Create and modify a temporary credential instead of one that
-	 * is potentially shared.  This could also mess up socket
-	 * buffer accounting which can run in an interrupt context.
+	 * is potentially shared.
 	 */
 	if (!(flags & AT_EACCESS)) {
 		cred = td->td_ucred;