Remove pre-2.2 Linux kernel support

[David Miller]

From: Andreas Jaeger <aj@suse.com>
Date: Mon, 14 May 2012 16:00:14 +0200

> David, I guess that after the change 
> sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c can be removed. Please 
> check this.

On what basis do you think it can be removed?

We need that special sigreturn assembler stub stuff on 32-bit sparc,
ragardless of whether rtsignals are available or not.