remove unused method

lib/model/txproposal.js

@@ -147,14 +147,10 @@ TxProposal.prototype._updateStatus = function() {
   }
 };
 
-TxProposal.newBitcoreTransaction = function() {
-  return new Bitcore.Transaction();
-};
-
 TxProposal.prototype._buildTx = function() {
   var self = this;
 
-  var t = TxProposal.newBitcoreTransaction();
+  var t = new Bitcore.Transaction();
 
   $.checkState(_.contains(_.values(Constants.SCRIPT_TYPES), self.addressType));