Use rm -rf to prevent silly questions from being asked

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5449 d4fa192b-c00b-0410-8231-f00ffab90ce4

doc/sphinx/Makefile.am

@@ -144,4 +144,4 @@ dist-hook:
 	cp -r $(BUILDDIR) $(distdir)
 
 distclean-local:
-	rm -r $(BUILDDIR)
+	rm -rf $(BUILDDIR)