system, remote-desktop: Use "rdp" instead of "ms-rd" for hostname url
According to https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/clients/remote-desktop-uri "The ms-rd URI scheme is currently only supported with the Windows Desktop client (MSRDC)."
Apps such as GNOME Connections and Remmina expect server hostname addresses using the "rdp" url scheme prefix.
See also #2827 (comment 1963502)
Fixes #1922 (closed)