smaller exception for Utf8JsonReader.GetBytesFromBase64

Author: carlossanlop

xml/System.Text.Json/Utf8JsonReader.xml

@@ -244,15 +244,7 @@ in more data asynchronously before continuing with a new instance of the <xref:S
         <returns>The byte array that represents the current JSON token value.</returns>
         <remarks>To be added.</remarks>
         <exception cref="T:System.InvalidOperationException">The type of the JSON token is not a <see cref="F:System.Text.Json.JsonTokenType.String" />.</exception>
-        <exception cref="T:System.FormatException">The JSON string contains data outside of the expected base 64 range.
-          
-- or -
-
-The JSON string contains invalid padding characters or more than two padding characters.
-
-- or -
-          
-The JSON string is incomplete; that is, the JSON string length is not a multiple of 4.</exception>
+        <exception cref="T:System.FormatException">The value is not encoded as base 64 text and hence cannot be decoded to bytes.</exception>
       </Docs>
     </Member>
     <Member MemberName="GetComment">