powerpc: remove meaningless KBUILD_ARFLAGS addition

The KBUILD_ARFLAGS addition in arch/powerpc/Makefile has never worked
in a useful way because it is always overridden by the following code
in the top Makefile:

  # use the deterministic mode of AR if available
  KBUILD_ARFLAGS := $(call ar-option,D)

The code in the top Makefile was added in 2011, by commit 40df759
("kbuild: Fix build with binutils <= 2.19").

The KBUILD_ARFLAGS addition for ppc has always been dead code from the
beginning.

Nobody has reported a problem since 43c9127 ("powerpc: Add option
to use thin archives"), so this code was unneeded.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190713032106.8509-1-yamada.masahiro@socionext.com

arch/powerpc/Makefile

@@ -112,7 +112,6 @@ ifeq ($(HAS_BIARCH),y)
 KBUILD_CFLAGS	+= -m$(BITS)
 KBUILD_AFLAGS	+= -m$(BITS) -Wl,-a$(BITS)
 KBUILD_LDFLAGS	+= -m elf$(BITS)$(LDEMULATION)
-KBUILD_ARFLAGS	+= --target=elf$(BITS)-$(GNUTARGET)
 endif
 
 cflags-$(CONFIG_STACKPROTECTOR)	+= -mstack-protector-guard=tls