[Wallet] Remove (explicitely) unused tx comparator
[Wallet] Remove (explicitely) unused tx comparator

We remove the '==' and '!=' operators from CMutableTransaction.
These comparators are never explicitely used in our code.
As it turns out, it was used implicitely and created this situation:
https://github.com/PIVX-Project/PIVX/issues/510
So this change fixes #510.

PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Mrs-X/PIVX,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/Darknet,Darknet-Crypto/Darknet