kconfig/lxdialog: fix make mrproper

No Makefile in scripts/kconfig/lxdialog anymore, so do not
go there during make mrproper.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index b2928f0..0b415eb 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -135,7 +135,6 @@
 
 clean-files	:= lkc_defs.h qconf.moc .tmp_qtcheck \
 		   .tmp_gtkcheck zconf.tab.c lex.zconf.c zconf.hash.c
-subdir- += lxdialog
 
 # Needed for systems without gettext
 KBUILD_HAVE_NLS := $(shell \