Small Rules.make cleanup

Get rid of long obsolete (and unused) MOD_IN_SUBDIRS and unnecessary
MOD_DIRS variable.

Rules.make

@@ -191,21 +191,19 @@ ifneq "$(strip $(obj-m))" ""
 MOD_DESTDIR := $(shell $(CONFIG_SHELL) $(TOPDIR)/scripts/pathdown.sh)
 endif
 
-unexport MOD_DIRS
-MOD_DIRS := $(MOD_SUB_DIRS) $(MOD_IN_SUB_DIRS)
-ifneq "$(strip $(MOD_DIRS))" ""
-.PHONY: $(patsubst %,_modsubdir_%,$(MOD_DIRS))
-$(patsubst %,_modsubdir_%,$(MOD_DIRS)) : dummy
+ifneq "$(strip $(MOD_SUB_DIRS))" ""
+.PHONY: $(patsubst %,_modsubdir_%,$(MOD_SUB_DIRS))
+$(patsubst %,_modsubdir_%,$(MOD_SUB_DIRS)) : dummy
 	$(MAKE) -C $(patsubst _modsubdir_%,%,$@) modules
 
-.PHONY: $(patsubst %,_modinst_%,$(MOD_DIRS))
-$(patsubst %,_modinst_%,$(MOD_DIRS)) : dummy
+.PHONY: $(patsubst %,_modinst_%,$(MOD_SUB_DIRS))
+$(patsubst %,_modinst_%,$(MOD_SUB_DIRS)) : dummy
 	$(MAKE) -C $(patsubst _modinst_%,%,$@) modules_install
 endif
 
 .PHONY: modules
 modules: $(obj-m) dummy \
-	 $(patsubst %,_modsubdir_%,$(MOD_DIRS))
+	 $(patsubst %,_modsubdir_%,$(MOD_SUB_DIRS))
 
 .PHONY: _modinst__
 _modinst__: dummy
@@ -216,7 +214,7 @@ endif
 
 .PHONY: modules_install
 modules_install: _modinst__ \
-	 $(patsubst %,_modinst_%,$(MOD_DIRS))
+	 $(patsubst %,_modinst_%,$(MOD_SUB_DIRS))
 
 #
 # A rule to do nothing