asm/user.h: killed unused macros

Some of them used to be used by libbfd for a.out coredump handling.
Seeing that
	* libbfd has their copies anyway
	* we don't export them into userland headers
	* we don't support a.out coredumps anymore
let's bury the definitions.  They never had in-kernel
users anyway...

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