[RFC] Remove zPIV controls from the GUI

[random-zebra]

Tracking issue for the removal of all functionalities related to the legacy Zerocoin privacy protocol from the GUI interface.
Starting from next wallet release, spending coins and checking zPIV balance should be only available through the RPC interface / console.

[Fuzzbawls]

PIVX Core v4.1.x is the last version to display zPIV information in the GUI. As such, and as mentioned above, this will in-turn remove the ability to spend any remaining zPIV directly in the GUI interface.

RPC availability for spending zPIV and getting zPIV balance information will remain until the v5.0.0 release, at which time we will no longer support the spending of zPIV with the core wallet at all.