Makefile: usbdux is an empty dir

It only contains source/README, which we remove in the installed
copy anyway.
Signed-off-by: Kyle McMartin <kyle@kernel.org>

Makefile

@@ -8,7 +8,6 @@ all:
 install:
 	mkdir -p $(DESTDIR)$(FIRMWAREDIR)
 	cp -r * $(DESTDIR)$(FIRMWAREDIR)
-	find $(DESTDIR)$(FIRMWAREDIR)/usbdux \( -name '*dux' -type f -or \
-		-name '*.asm' \) -exec rm -- {} \;
+	rm -rf $(DESTDIR)$(FIRMWAREDIR)/usbdux
 	find $(DESTDIR)$(FIRMWAREDIR) \( -name 'WHENCE' -or -name 'LICENSE.*' -or \
 		-name 'LICENCE.*' \) -exec rm -- {} \;