Remove unused fork implementations

[David Miller]

From: Roland McGrath <roland@hack.frob.com>
Date: Tue, 24 Apr 2012 16:39:16 -0700 (PDT)

>> That leaves sysdeps/unix/sparc/sysdep.h which is used, by:
>> 
>> 	sysdeps/unix/sysv/linux/sparc/sparc32/sysdep.h
>> 	sysdeps/unix/sysv/linux/sparc/sparc64/sysdep.h
>> 
>> Should I move the contents of sysdeps/unix/sparc/sysdep.h into
>> sysdeps/sparc/sysdep.h?
>> 
>> The PIC bits are OS neutral, but the system call stuff is "UNIX"
>> specific.
>> 
>> So, maybe put the PIC bits into sysdeps/sparc/sysdep.h and put the
>> syscall stuff into sysdeps/unix/sysv/linux/sparc/sysdep.h?
> 
> Each area of code should be in the least-specific sysdeps directory to
> which it applies.  So moving things purely about writing sparc machine
> code into sysdeps/sparc/ is right.  If the syscall stuff applies to how
> syscalls are done on other sparc systems like BSDs, then leave it in
> sysdeps/unix/sparc/.

I looked more closely at this situation and everything in
sysdeps/unix/sparc/sysdep.h either belongs in sysdeps/sparc/sysdep.h
or is completely overridden by Linux/sparc.

Therefore the file is useless and I'll remove it, along with the rest
of the sysdeps/unix/sparc files which have already been found to be
completely unused.