Removing unused property

Post::Subreddit property was only used in the set flair method. Since it was
not required there, it can be removed. It was a public property so this may
break consumers if they were trying to get something, what I don't know, out
of it.

Author: epvanhouten

RedditSharp/Things/Post.cs

@@ -116,9 +116,6 @@ public Comment[] Comments
         [JsonProperty("selftext_html")]
         public string SelfTextHtml { get; set; }
 
-        [JsonProperty("subreddit")]
-        public string Subreddit { get; set; }
-
         [JsonProperty("thumbnail")]
         [JsonConverter(typeof(UrlParser))]
         public Uri Thumbnail { get; set; }