kbuild: do not deduplicate modules.order

The AWK code was added to deduplicate modules.order in case $(obj-m)
contains the same module multiple times, but it is actually unneeded
since commit b2c88554 ("kbuild: update modules.order only when
contained modules are updated").

The list is already deduplicated before being processed by AWK because
$^ is the deduplicated list of prerequisites.
(Please note the real-prereqs macro uses $^)

Yet, modules.order will contain duplication if two different Makefiles
build the same module:

  foo/Makefile:

      obj-m += bar/baz.o

  foo/bar/Makefile:

      obj-m += baz.o

However, the parallel builds cannot properly handle this case in the
first place. So, it is better to let it fail (as already done by
scripts/modules-check.sh).
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1430,14 +1430,11 @@ endif
 
 # Build modules
 #
-# A module can be listed more than once in obj-m resulting in
-# duplicate lines in modules.order files.  Those are removed
-# using awk while concatenating to the final file.
 
 PHONY += modules
 modules: $(if $(KBUILD_BUILTIN),vmlinux) modules_check modules_prepare
 
-cmd_modules_order = $(AWK) '!x[$$0]++' $(real-prereqs) > $@
+cmd_modules_order = cat $(real-prereqs) > $@
 
 modules.order: $(subdir-modorder) FORCE
 	$(call if_changed,modules_order)

scripts/Makefile.build

@@ -374,7 +374,7 @@ $(obj)/built-in.a: $(real-obj-y) FORCE
 
 cmd_modules_order = { $(foreach m, $(real-prereqs), \
 	$(if $(filter %/modules.order, $m), cat $m, echo $(patsubst %.o,%.ko,$m));) :; } \
-	| $(AWK) '!x[$$0]++' - > $@
+	> $@
 
 $(obj)/modules.order: $(obj-m) FORCE
 	$(call if_changed,modules_order)