Makefile: Remove --prune option to source preparation

The option --prune is not available anymore in setup.py.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

Makefile

@@ -29,7 +29,7 @@ prepare-source:
 	# build the source package in the parent directory
 	# then rename it to project_version.orig.tar.gz
 	dch -D "utopic" -M -v "$(VERSION)" "Automated (make builddeb) build."
-	$(PYTHON) setup.py sdist $(COMPILE) --dist-dir=../ --prune
+	$(PYTHON) setup.py sdist $(COMPILE) --dist-dir=../
 	rename -f 's/$(PROJECT)-(.*)\.tar\.gz/$(PROJECT)_$$1\.orig\.tar\.gz/' ../*
 
 build-deb-src: prepare-source