kbuild: remove obj-n and lib-n handling

Kconfig never defines CONFIG_* as 'n'.
Now obj-n is only used in firmware/Makefile and it can be
replaced with obj-.  No makefile uses lib-n.

Let's rip off obj-n and lib-n.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Peter Foley <pefoley2@pefoley.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
index a651cee..c630ab5 100644
--- a/scripts/Makefile.clean
+++ b/scripts/Makefile.clean
@@ -23,15 +23,13 @@
 subdir-y	+= $(__subdir-y)
 __subdir-m	:= $(patsubst %/,%,$(filter %/, $(obj-m)))
 subdir-m	+= $(__subdir-m)
-__subdir-n	:= $(patsubst %/,%,$(filter %/, $(obj-n)))
-subdir-n	+= $(__subdir-n)
 __subdir-	:= $(patsubst %/,%,$(filter %/, $(obj-)))
 subdir-		+= $(__subdir-)
 
 # Subdirectories we need to descend into
 
 subdir-ym	:= $(sort $(subdir-y) $(subdir-m))
-subdir-ymn      := $(sort $(subdir-ym) $(subdir-n) $(subdir-))
+subdir-ymn      := $(sort $(subdir-ym) $(subdir-))
 
 # Add subdir path