kbuild: hardcode genksyms path and remove GENKSYMS variable

The genksyms source was integrated into the kernel tree in 2003.

I do not expect anybody still using the external /sbin/genksyms.
Kbuild does not need to provide the ability to override GENKSYMS.

Let's remove the GENKSYMS variable, and use the hardcoded path.

Since it occurred in the pre-git era, I attached the commit message
in case somebody is interested in the historical background.

  | Author: Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
  | Date:   Wed Feb 19 04:17:28 2003 -0600
  |
  | kbuild: [PATCH] put genksyms in scripts dir
  |
  | This puts genksyms into scripts/genksyms/.
  |
  | genksyms used to be maintained externally, though the only possible user
  | was the kernel build. Moving it into the kernel sources makes it easier to
  | keep it uptodate, like for example updating it to generate linker scripts
  | directly instead of postprocessing the generated header file fragments
  | with sed, as we do currently.
  |
  | Also, genksyms does not handle __typeof__, which needs to be fixed since
  | some of the exported symbol in the kernel are defined using __typeof__.
  |
  | (Rusty Russell/me)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index 498b6c5..7d9032b 100644
--- a/Makefile
+++ b/Makefile
@@ -390,7 +390,6 @@
 LEX		= flex
 YACC		= bison
 AWK		= awk
-GENKSYMS	= scripts/genksyms/genksyms
 INSTALLKERNEL  := installkernel
 DEPMOD		= /sbin/depmod
 PERL		= perl
@@ -443,7 +442,7 @@
 
 export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS
-export MAKE LEX YACC AWK GENKSYMS INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE
+export MAKE LEX YACC AWK INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE
 export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS