Fix attachment size

This is already a number.

// FREEBIE

js/libtextsecure.js

@@ -38538,9 +38538,6 @@ MessageReceiver.prototype.extend({
     handleAttachment: function(attachment) {
         attachment.id = attachment.id.toString();
         attachment.key = attachment.key.toArrayBuffer();
-        if (attachment.size) {
-            attachment.size = attachment.size.toNumber();
-        }
         if (attachment.digest) {
           attachment.digest = attachment.digest.toArrayBuffer();
         }

libtextsecure/message_receiver.js

@@ -344,9 +344,6 @@ MessageReceiver.prototype.extend({
     handleAttachment: function(attachment) {
         attachment.id = attachment.id.toString();
         attachment.key = attachment.key.toArrayBuffer();
-        if (attachment.size) {
-            attachment.size = attachment.size.toNumber();
-        }
         if (attachment.digest) {
           attachment.digest = attachment.digest.toArrayBuffer();
         }