Delete AccountManager.java

This file was never used by anyone. RIP.

src/main/java/emu/grasscutter/game/managers/AccountManager.java

-package emu.grasscutter.game.managers;
-
-import emu.grasscutter.server.game.GameServer;
-
-public class AccountManager {
-	private final GameServer server;
-	
-	public AccountManager(GameServer server) {
-		this.server = server;
-	}
-
-	public GameServer getServer() {
-		return server;
-	}
-}