stop including username in login block

customize.dist/login.js

@@ -99,7 +99,6 @@ define([
         opt.channelHex = parsed.channel;
         opt.keys = parsed.keys;
         opt.edPublic = blockInfo.edPublic;
-        opt.User_name = blockInfo.User_name; // XXX do we actually use this? can we drop it?
         return opt;
     };
 

www/common/cryptpad-common.js

@@ -2068,7 +2068,6 @@ define([
         }).nThen(function (waitFor) {
             // Write the new login block
             var temp = {
-                User_name: accountName,
                 User_hash: newHash,
                 edPublic: edPublic,
             };