As described on the Microsoft Support website -- https://support.microsoft.com/en-us/help/2673231/how-to-control-the-room-finder-in-outlook, an update of the Microsoft Exchange Add-in added an option to completely disable the default Room Finder by adding the following registry entry. This change keeps the default room finder hidden also on the Scheduling Assistant view.

Outlook 2010 Location: HKCU\Software\Microsoft\Office\14.0\Outlook\Preferences
Outlook 2013 Location: HKCU \Software\Microsoft\Office\15.0\Outlook\Preferences
Outlook 2016 Location: HKCU \Software\Microsoft\Office\16.0\Outlook\Preferences

Name - Type - Value
RoomFinderForceDisabled - REG_DWORD - 1

I suggest adding this to the Outlook Plugin MSI installer.