sparc32: kill lookup_fault()

No callers left.  As the result we can kill
	* lookup_fault() itself
	* the kludge in do_sparc_fault() for passing the
arguments for eventual lookup_fault() into exception handler and
labels used by it
	* the last of magical exception table entries (in __clear_user())

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>