Remove dead IWsServer interface

It was defined but never used as a type and not inherited by
WsServerMultiUser. Also removes the now-unused abc import.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tqxrk8uj4M3w3d3eXm3xK8

ws/server/ws_server_multi_user.py

@@ -1,20 +1,9 @@
 import asyncio
 from ws.server.ws_server import WsServer
 from ws.user import User, UserSet, update
-import abc
 from ws.connection import IConnection
 
 
-class IWsServer:
-	@abc.abstractmethod
-	def on_recv(self, data, loop):
-		pass
-
-	@abc.abstractmethod
-	def on_send(self, loop):
-		pass
-
-
 class WsServerMultiUser(WsServer):
 	def __init__(self, loop=None, listener: IConnection = None):
 		WsServer.__init__(self, loop)