Remove the 'macosx' arch

Remove the 'macosx' arch

The new atomic implementation chooses which header to include based
on what #define's are set by the compiler (i.e. __x86_64__ or
__i386__). Because of this, the qatomic_macosx.h header isn't used
anymore. This also means that the configure script does not need to
use or look for this file anymore, it should just use the normal
uname -m detection.

Change-Id: Ibf275488735483268286196952299c0e496dfd1f
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>