rpc: Do not require a privkey corresponding to ownerAddress in `protx register_*` to be known by the wallet (#3773)
rpc: Do not require a privkey corresponding to ownerAddress in `protx register_*` to be known by the wallet (#3773)

This requirement was introduced in the initial implementation when we were signing protx payload with the owner key (#2246). This was changed later when we implemented external collateral references (#2366). The owner key is not used for anything in ProTxReg but to get CKeyID since then which we can do by simply decoding an address instead. This simplifies masternode registration process by letting an Operator to issue `protx register_prepare` on its own instead of asking an Owner. An Owner still have to sign the message provided by an Operator with his collateral address to prove collateral ownership (and authorize masternode registration).

Note: `protx register_*` rpc will no longer accept privkeys for ownerAddress. Some 3-rd party software like DMT might need to be patched to work correctly with nodes running with this fix.

Former-commit-id: d1a000e6d5a360ad8ebcedbf317679a6212cb3a4
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin