[ZIPs 226, 227] Move rule about `nActionGroupsOrchard` and `nAGExpiryHeight` from ZIP 227 to ZIP 226

[daira]

For every transaction:

• The nActionGroupsOrchard field MUST have a value of either 0 or 1 and the nAGExpiryHeight field MUST have a value of 0.

This belongs in 226 because it is a rule about transfers, not issuance.