RestGuild#DefaultChannelId will fall back to the guild ID

Adding an exception here would be a breaking change, so this was agreed
to fall back to the previous behavior, which would just return the guild
ID.

src/Discord.Net.Rest/Entities/Guilds/RestGuild.cs

@@ -33,9 +33,9 @@ namespace Discord.Rest
         internal bool Available { get; private set; }
 
         public DateTimeOffset CreatedAt => SnowflakeUtils.FromSnowflake(Id);
+
         [Obsolete("DefaultChannelId is deprecated, use GetDefaultChannelAsync")]
-        public ulong DefaultChannelId =>
-            throw new NotSupportedException("DefaultChannelId can not be accessed synchronously, see GetDefaultChannelAsync");  
+        public ulong DefaultChannelId => Id;
         public string IconUrl => CDN.GetGuildIconUrl(Id, IconId);
         public string SplashUrl => CDN.GetGuildSplashUrl(Id, SplashId);