kbuild: remove redundant FORCE definition in scripts/Makefile.modpost

The same code exists a few lines above.

Fixes: 436b2ac6 ("modpost: invoke modpost only when input files are updated")
Signed-off-by: NMasahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.modpost

@@ -124,9 +124,6 @@ existing-targets := $(wildcard $(sort $(targets)))
 
 -include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
 
-PHONY += FORCE
-FORCE:
-
 endif
 
 .PHONY: $(PHONY)