Makefile: Don't fail remove when extension isn't installed

Currently `make remove` fails if the extension isn't installed, but it
makes more sense for the removal operation to just succeed quietly if the
extension isn't there.

Fixes #102

Makefile

@@ -102,7 +102,7 @@ install: remove build
 remove:
 	$(call msg,$@,$(SUDO) $(INSTALLBASE)/$(INSTALLNAME))
 ifeq ($(strip $(BUILD_FOR_RPM)),)
-	$(Q) gnome-extensions uninstall $(UUID)
+	$(Q) gnome-extensions uninstall --quiet $(UUID) || true
 endif
 	$(call msg,$@,OK)