openwrt: Clean up build input setup, forcing user to set it up

This makes it so that if the inputs are not available -- namely
input/.config and possibly input/files/, the build won't run. This
helps inform the user what must be done in order to get things to
build.

openwrt/Makefile

@@ -13,26 +13,16 @@ ifndef INC_DOCKER
 include ${docker_src}/Makefile
 endif
 
-.PHONY: input
-input:
-	rm -rf input; mkdir -p input; chmod 777 input;
+input/:
+	rm -rf input; mkdir input; chmod 777 input;
 
 .PHONY: prep-output
 prep-output:
 	rm -rf output; mkdir output; chmod 777 output;
 
-diffconfig:
-	touch $@;
-
-input/.config: diffconfig input
+input/.config: diffconfig input/
 	cp $< $@
 
-files/:
-	-rm -r $@; mkdir -p $@;
-
-input/files/: files/
-	cp -r $< $@
-
 BASE_REQS := prep-output input/.config input.sh output.sh input/files/
 
 output: ${docker_src}/built/openwrt-builder-master.sentinel $(BASE_REQS)