Remove the ability to disable the check that a specified fee is equal to the unspent value.

lib/transaction/transaction.js

@@ -197,14 +197,15 @@ Transaction.prototype.getSerializationError = function(opts) {
   }
 
   var feeIsDifferent = this._isFeeDifferent();
+  if (feeIsDifferent) {
+    return new errors.Transaction.FeeError.Different(feeIsDifferent);
+  }
+
   var missingChange = this._missingChange();
   var feeIsTooLarge = this._isFeeTooLarge();
   var feeIsTooSmall = this._isFeeTooSmall();
   var isFullySigned = this.isFullySigned();
 
-  if (!opts.disableDifferentFees && feeIsDifferent) {
-    return new errors.Transaction.FeeError.Different(feeIsDifferent);
-  }
   if (!opts.disableLargeFees && feeIsTooLarge) {
     if (missingChange) {
       return new errors.Transaction.ChangeAddressMissing('Fee is too large and no change address was provided');