kbuild: remove old check for CFLAGS use

This check has been here for more than a decade since
commit 0c53c8e6eb ("kbuild: check for wrong use of CFLAGS").

Enough time for migration has passed.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.build

@@ -36,21 +36,11 @@ subdir-ccflags-y :=
 
 include scripts/Kbuild.include
 
-# For backward compatibility check that these variables do not change
-save-cflags := $(CFLAGS)
-
 # The filename Kbuild has precedence over Makefile
 kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))
 kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)
 include $(kbuild-file)
 
-# If the save-* variables changed error out
-ifeq ($(KBUILD_NOPEDANTIC),)
-        ifneq ("$(save-cflags)","$(CFLAGS)")
-                $(error CFLAGS was changed in "$(kbuild-file)". Fix it to use ccflags-y)
-        endif
-endif
-
 include scripts/Makefile.lib
 
 # Do not include host rules unless needed