remove `HTTP RPC server` and remove outdated CLI options.

[niklasad1]

After #12663 was merged the RPC server supports WS/HTTP on the same socket and the HTTP server was kept for backwards compatibility.

However, we haven't provided any migration guidance.

Personally I think the way forward is as follows:

• Remove the HTTP server on port 9933 (this will break all cURL examples though)
• Make the default RPC port 9944 (same as the ws-server default, as it's recommend to interact with substrate via polkadot-js etc)
• Remove/rename all websocket/http specific options

The CLI options that will be removed/or renamed are:

• rpc_max_payload (replaced by rpc_max_request_size and rpc_max_response_size)
• ws_max_out_buffer_capacity
• ws_external
• unsafe_ws_external
• ipc_path
• ws_port (replaced by rpc_port)
• ws_max_connections (replaced by rpc_max_connections)

Thus, unfortunately this is a breaking change but it will simplify the configurations I think it's worth it in this case because the ws flags are not exclusively ws anymore.

Thoughts or suggestions?

/cc @PierreBesson @BulatSaif