steam: update generated runtime dependencies

The referenced zenity URL wasn't valid anymore:

trying http://repo.steampowered.com/steamrt/pool/main/z/zenity/zenity_3.4.0-0ubuntu4+steamrt2+srt6_amd64.deb
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (22) The requested URL returned error: 404 Not Found