LegacyMsg in payment module deprecated in favor of Msg Services

[mpoke]

For executing MsgPayForData messages, the payment module implements a handler function, which is added to the application's router via the Route() method. This is deprecated (see https://docs.cosmos.network/v0.45/building-modules/msg-services.html#amino-legacymsgs).

Suggestions:

• register the message server, i.e.,

func (am AppModule) RegisterServices(cfg module.Configurator) {
	types.RegisterMsgServer(cfg.MsgServer(), keeper.NewMsgServerImpl(am.keeper))
	// ...
}

• return an empty route in Route()

func (am AppModule) Route() sdk.Route {
	return sdk.Route{}
}

• delete x/payment/handler.go

Further suggestions for improving code quality:

Note that these changes will make the structure of the module consistent with the SDK.

• move msgServer methods to x/payment/keeper/msg_server.go, i.e., PayForData method
• create x/payment/types/msgs.go file that contains the two message types (i.e., MsgWirePayForData, MsgPayForData) together with their functions