Writing through the lg::wml log domain isn't equivalent to putting stuff...

...at the end of the lg::wml_error stringstream... why label a commit
like part of a different refactoring task if it also has these
unrelated side-effects?

src/intro.cpp

@@ -39,7 +39,7 @@ static void scan_deprecation_messages(const config &cfg)
 	{
 		const std::string &msg = child["message"];
 		if (msg.empty()) continue;
-		LOG_STREAM(err, wml) << msg << '\n';
+		lg::wml_error << msg << '\n';
 	}
 }