powerpc: Remove dead code in sycall entry

In:
  commit 742415d6
  Author: Michael Neuling <mikey@neuling.org>
  powerpc: Turn syscall handler into macros

We converted the syscall entry code onto macros, but in doing this we
introduced some cruft that's never run and should never have been added.

This removes that code.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>