Remove unused SERVICE_FLAG

[kostyantyn]

Is your feature request related to a problem? Please describe Since we cloned the code from Bitcoin, we also inherited service flags that can be turned on/off. For instance, NODE_WITNESS which indicates if the node can provide witness data however it's a default condition for our node. Receiving the request that says node doesn't support witness data doesn't make sense. However, we can keep it as to be "better" compatible with the bitcoin codebase (exactly codebase as the protocol is not backward compatible)

Describe the solution you'd like I'd remove service flags that can't be turned off or those that are for historical reason NODE_GETUTXO. It will also require to adjust the code in https://github.com/dtr-org/unit-e-seeder

Describe alternatives you've considered Alternatively, we can ban the node which turns off such feature flags and remove the code which is responsible for such scenarios to not end up in "undefined behavior" :)