Remove pointless .Net 5 remark (dotnet#7464)

Author: svick

xml/System.Net.Http/HttpRequestException.xml

@@ -203,7 +203,6 @@
       <Docs>
         <summary>Gets the HTTP status code to be returned with the exception.</summary>
         <value>An HTTP status code if the exception represents a non-successful result, otherwise <c>null</c>.</value>
-        <remarks>This property was introduced in .NET 5.</remarks>
       </Docs>
     </Member>
   </Members>