Backport Core PR10683: rpc: Move the generate RPC call to rpcwallet
2a96283 rpc: Update `generate` for developer notes (Wladimir J. van der Laan) df7e2f0 rpc: Move the `generate` RPC call to rpcwallet (Wladimir J. van der Laan)
This makes it possible to mine to any wallet when multi-wallet mode is added.
Solves the same problem as #10649, but IMO in a cleaner way.
It also gets rid of the circuitous ScriptForMining method on
CValidationInterface, which really doesn't belong there.
After this change it's still possible to mine without wallet through