Code cleanup

Author: MaggieKimani1

src/Microsoft.OpenApi.Readers/OpenApiStreamReader.cs

@@ -45,15 +45,17 @@ public OpenApiDocument Read(Stream input, out OpenApiDiagnostic diagnostic)
             var reader = new StreamReader(input);
             var result = new OpenApiTextReaderReader(_settings).Read(reader, out diagnostic);
 
-            HashAlgorithm sha = SHA512.Create();
-            byte[] data = sha.ComputeHash(input);
-            StringBuilder sb = new StringBuilder();
-            for (int i = 0; i < data.Length; i++)
-            {
-                sb.Append(data[i].ToString("X2"));
-            }
+            //HashAlgorithm sha = SHA512.Create();
+            //byte[] data = sha.ComputeHash(input);
+            //StringBuilder sb = new StringBuilder();
+            //for (int i = 0; i < data.Length; i++)
+            //{
+            //    sb.Append(data[i].ToString("X2"));
+            //}
+            
 
-            diagnostic.HashCode = sb.ToString();
+            //diagnostic.HashCode = sb.ToString();
+            diagnostic.HashCode = OpenApiDocument.GenerateHashValue(input);
 
             if (!_settings.LeaveStreamOpen)
             {