Remove unused fork implementations

[Joseph S. Myers]

On Tue, 24 Apr 2012, Roland McGrath wrote:

> It's still possible to configure for *-linux-gnu without nptl
> (given --disable-sanity), in which case those files would be used.

The sysdeps/unix files still wouldn't be used because fork is in 
sysdeps/unix/sysv/linux/syscalls.list, which will take precedence.  I 
guess this case is relevant to the removal of 
sysdeps/unix/sysv/linux/sparc/fork.S (and the IA64 version in ports), 
though - David, should that file be kept on that basis, or is removing 
both SPARC versions of fork.S OK?

-- 
Joseph S. Myers
joseph@codesourcery.com