SSO has to be initiated somewhere.  Normally that would be done from an SSO portal/landing page with all your apps on it.  Clicking on the Screenconnect link would take you directly to being logged in without using the login page at all.  I've tested that, it does work.  The larger issue with options on the login page is user confusion, or on the flip side if you have multiple external providers, leaking information about your clients and what login options are available.  I've changed my login page to remove those, as opposed to removing the L/P.

If you're really desperate to remove the L/P prompt, you should be able to comment out the part of login.aspx that displays it.  Should be lines 84-92 or thereabouts depending on your version.

Starting at: "$form({ _commandName: 'SubmitLogin' }, ["

Ending at:  "])," that's indented to the same level.