Remove stddef.h configure test

[Florian Weimer]

On 10/15/2015 07:01 PM, Joseph Myers wrote:
> 2015-10-15  Joseph Myers  <joseph@codesourcery.com>
> 
> 	* configure.ac (libc_cv_friendly_stddef): Remove configure test.
> 	* configure: Regenerated.

Okay for master.

Thanks,
Florian