sparc: bury a zombie extern that had been that way for twenty years

Back in January 1998, in 2.1.79 check_pending() got taken out and shot.
Users in arch/sparc and arch/sparc64 got converted away from it.  One
of the externs (in arch/sparc) was taken out at the same time.  Two
other (in arch/sparc64/kernel/sys_sparc{,32}.c) got stuck.  The one in
sys_sparc32.c was quietly removed 6 years later by an unrelated
commit.  The last one kept shambling until now.  It's time to end
that depravity, let's bury the body...

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