drafts: Remove unused localstorage version.

It's been present since 1929cc5 and clearly is intended
to be part of a never-implemented format conversion
system. We can add a version if/when we actually need
such a feature.

web/src/drafts.js

@@ -32,7 +32,6 @@ export const draft_model = (function () {
     // the key that the drafts are stored under.
     const KEY = "drafts";
     const ls = localstorage();
-    ls.version = 1;
 
     function getTimestamp() {
         return Date.now();