Remove reference to InvalidOperationException (#2657)

Uri.OriginalString does not throw InvalidOperationException if a relative URI is used. This is true for .NET Core 3.0+ (at least) and the .NET Framework 4.8 (via ReferenceSource).

Sources: https://github.com/dotnet/corefx/blob/e2b4dc93c9f9482b67f962106937d4fdd46f5673/src/System.Private.Uri/src/System/Uri.cs#L1145-L1153
https://referencesource.microsoft.com/#System/net/System/URI.cs,1234

Author: watfordgnf

xml/System/Uri.xml

@@ -3561,7 +3561,6 @@ If you used an escaped string to construct this instance (for example, `"http://
   
  ]]></format>
         </remarks>
-        <exception cref="T:System.InvalidOperationException">This instance represents a relative URI, and this property is valid only for absolute URIs.</exception>
       </Docs>
     </Member>
     <Member MemberName="Parse">