get rid of unneccesary field and property added

Author: Jasmine

src/GitHub.Exports/Primitives/UriString.cs

@@ -77,7 +77,6 @@ void SetUri(Uri uri)
             }
 
             IsHypertextTransferProtocol = uri.IsHypertextTransferProtocol();
-            IsGithubUri = uri.IsGithubUri();
         }
 
         void SetFilePath(Uri uri)

src/GitHub.Extensions/UriExtensions.cs

@@ -25,11 +25,6 @@ public static bool IsHypertextTransferProtocol(this Uri uri)
             return uri.Scheme == "http" || uri.Scheme == "https";
         }
 
-        public static bool IsGithubUri(this Uri uri)
-        {
-            return uri.OriginalString.Contains("github.com");
-        }
-
         public static bool IsSameHost(this Uri uri, Uri compareUri)
         {
             return uri.Host.Equals(compareUri.Host, StringComparison.OrdinalIgnoreCase);