kbuild: Makefile: remove unnecessary check for m68knommu ARCH

ARCH is never set to m68knomm.
make ARCH=m68knomm is not supported anymore.

Signed-off-by: Edward Shao <laface.tw@gmail.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -231,10 +231,6 @@ endif
 # Where to locate arch specific headers
 hdr-arch  := $(SRCARCH)
 
-ifeq ($(ARCH),m68knommu)
-       hdr-arch  := m68k
-endif
-
 KCONFIG_CONFIG	?= .config
 export KCONFIG_CONFIG