build: remove artefacts on distclean

since .pkg-files already lives in out/ they're already gone. instead of
moving artefacts into out/ (which might mess with upload scripts),
delete their current location.

PR-URL: #323
Reviewed-By: Rod Vagg <rod@vagg.org>

Makefile

@@ -68,6 +68,7 @@ distclean:
 	-rm -rf node_modules
 	-rm -rf deps/icu
 	-rm -rf deps/icu4c*.tgz deps/icu4c*.zip deps/icu-tmp
+	-rm -f $(BINARYTAR).* $(TARBALL).*
 
 test: all
 	$(PYTHON) tools/test.py --mode=release message parallel sequential -J