From

Digging into SOAP Headers with the .NET Framework
:

If you don’t want to disable the ASP.NET auto-generated WSDL
from your web service (so that you can replace it with a static
document):

…you might want to disable the ?WSDL functionality for your
Web service. You can do this by manipulating the web.config file to
remove the “Documentation” protocol for Web services. The crucial
part of the web.config that removes WSDL documentation is shown
below:

<system.web>
  <webServices>
    <protocols>
      <remove name="Documentation"/>
    </protocols>
  </webServices>
</system.web>