kbuild: re-enable KCSAN for autogenerated *.mod.c intermediaries

This reverts commit 54babdc ("kbuild: Disable KCSAN for
autogenerated *.mod.c intermediaries").

Now that objtool is enabled for *.mod.c, there is no need to filter
out CFLAGS_KCSAN.

I no longer see "Unpatched return thunk in use. This should not happen!"
error with KCSAN when loading a module.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Author: masahir0y

scripts/Makefile.modfinal

@@ -20,7 +20,6 @@ __modfinal: $(modules:%.o=%.ko)
 modname = $(notdir $(@:.mod.o=))
 part-of-module = y
 GCOV_PROFILE := n
-KCSAN_SANITIZE := n
 ccflags-remove-y := $(CC_FLAGS_CFI)
 
 %.mod.o: %.mod.c FORCE