[Refactoring] Skip expensive ContainsZerocoins/HasZerocoinSpendInputs
[Refactoring] Skip expensive ContainsZerocoins/HasZerocoinSpendInputs

...calls in ConnectBlock when possible.

The check at line 2798 in CheckBlock ensures that no zc tx (either mint
or spend) is accepted in the chain after v5 activation.
`ContainsZerocoins`/`HasZerocoinSpendInputs` are expensive functions,
especially when they return `false` (as they need to go through all
inputs and outputs).
Therefore avoid the duplicated check in ConnectBlock, and, instead, use
the shortcut operator to skip HasZerocoinSpendInputs call after v5
enforcement.

Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet