android: improve update rule

Remove old in-tree build artifacts that could conflict (`assets/libs` & `assets/module`).

make/android.mk

@@ -68,6 +68,8 @@ update: all
 	# Note: do not remove the module directory so there's no need
 	# for `mk7z.sh` to always recreate `assets.7z` from scratch.
 	rm -rf $(ANDROID_LIBS)
+	# Remove old in-tree build artifacts that could conflict.
+	rm -rf $(ANDROID_LAUNCHER_DIR)/assets/{libs,module}
 	# APK version
 	mkdir -p $(ANDROID_ASSETS)/module $(ANDROID_LIBS)
 	echo $(VERSION) >$(ANDROID_ASSETS)/module/version.txt