make_and_push_dated_tag: just push the tag we created, not all tags

In theory we should now be pushing all the tags we create, so why do
we even need this:

    # and push any tags that might have been created
    push_timings("gdt_push_tags");
    push_tags( $remote_site );

    exit(0);

But just push the tag we created here, if there's any leftover ones
for some reason they'll be picked up by the above code.