Removing groups from chatters when deleting groups.

Chat/Groups/ChatterGroupManager.cs

@@ -87,7 +87,13 @@ namespace TwitchChatTTS.Chat.Groups
 
         public bool Remove(string groupId)
         {
-            return _groups.Remove(groupId);
+            if (_groups.Remove(groupId))
+            {
+                foreach (var entry in _chatters)
+                    entry.Value.Remove(groupId);
+                return true;
+            }
+            return false;
         }
 
         public bool Remove(long chatterId, string groupId)