docs/architecture: Remove long-outdated bit.

There's a lot more that could be improved in this doc; at
zulip#3307 (comment),
we noted that we don't want to keep an up-to-date doc of everything
in the /src directory; everything should be done inline.

docs/architecture.md

@@ -49,7 +49,7 @@ persisted data.
 
 In general most of the work will be inside of the `/src` directory. The only
 reason to touch the `/ios` or `/android` directories would be to add native
-modules (which we aren't using at the moment).
+modules.
 
 ### Top-level files
 * `package.json` - specifies `yarn` / NPM dependencies and scripts for the project