Fixed several issues in ref entities

ref/Events/ChannelEventArgs.cs

@@ -4,7 +4,6 @@ namespace Discord
 {
     public class ChannelEventArgs : EventArgs
     {
-        public Channel Channel => null;
-        public Server Server => null;
+        public IChannel Channel => null;
     }
 }

ref/Events/ChannelUpdatedEventArgs.cs

@@ -6,6 +6,5 @@ namespace Discord
     {
         public IChannel Before => null;
         public IChannel After => null;
-        public Server Server => null;
     }
 }

ref/Events/MessageEventArgs.cs

@@ -6,7 +6,6 @@ namespace Discord
     {
         public Message Message => null;
         public User User => null;
-        public Channel Channel => null;
-        public Server Server => null;
+        public ITextChannel Channel => null;
     }
 }

ref/Events/MessageUpdatedEventArgs.cs

@@ -7,7 +7,6 @@ namespace Discord
         public Message Before => null;
         public Message After => null;
         public User User => null;
-        public Channel Channel => null;
-        public Server Server => null;
+        public ITextChannel Channel => null;
     }
 }

ref/Events/UserEventArgs.cs

@@ -4,6 +4,5 @@ namespace Discord
     public class UserEventArgs : EventArgs
     {
         public User User => null;
-        public Server Server => null;
     }
 }

ref/Events/UserUpdatedEventArgs.cs

@@ -5,6 +5,5 @@ namespace Discord
     {
         public User Before => null;
         public User After => null;
-        public Server Server => null;
     }
 }