Fix a few warnings.

osu.Game/GameModes/Menu/MainMenu.cs

@@ -12,7 +12,7 @@ internal class MainMenu : GameMode
     {
         public override string Name => @"Main Menu";
 
-        private AudioTrackBass bgm;
+        //private AudioTrackBass bgm;
 
 		public override void Load()
 		{

osu.Game/Online/API/SecurePassword.cs

@@ -2,6 +2,7 @@
 //Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
 using System;
+using System.Diagnostics;
 using System.Security;
 using osu.Framework.Extensions;
 
@@ -35,6 +36,8 @@ public SecurePassword(string input, bool encrypted = false)
 
         internal string Get(Representation request = Representation.Raw)
         {
+            Debug.Assert(representation == request);
+
             switch (request)
             {
                 default:

osu.Game/Online/Chat/Channel.cs

@@ -22,7 +22,7 @@ public class Channel
 
         public List<Message> Messages = new List<Message>();
 
-        internal bool Joined;
+        //internal bool Joined;
 
         [JsonConstructor]
         public Channel()

osu.Game/Online/Chat/Message.cs

@@ -21,10 +21,10 @@ public class Message
         public DateTime Timestamp;
 
         [JsonProperty(@"content")]
-        internal string Content;
+        public string Content;
 
         [JsonProperty(@"sender")]
-        internal string User;
+        public string User;
 
         [JsonConstructor]
         public Message()