Description:

xpra requires the Xprg command, which is provided by xorg-server. Without Xorg, xpra sessions cannot start:

2022-02-17 21:54:59,627 keyboard settings: rules=evdev, model=pc105, layout=us
2022-02-17 21:54:59,630 desktop size is 3840x2160 with 1 screen:
2022-02-17 21:54:59,631 :0.0 (591x332 mm - DPI: 165x165)
2022-02-17 21:54:59,631 SHP eDP1 (350x190 mm - DPI: 279x289)
2022-02-17 21:55:00,223 SSH: 'Entering daemon mode; any further errors will be reported to:'
2022-02-17 21:55:00,223 SSH: ' /run/user/1000/xpra/S539.log'
2022-02-17 21:55:19,876 SSH: 'Error: displayfd failed'
2022-02-17 21:55:19,878 SSH: ' did not provide a display number using displayfd'
2022-02-17 21:55:29,449 connection timed out
2022-02-17 21:55:29,453 Warning: printer forwarding disabled:
2022-02-17 21:55:29,453 No module named 'cups'
2022-02-17 21:55:29,459 SSH EOF on stderr of run-xpra
2022-02-17 21:55:29,469 removing unix domain socket '/run/user/1000/xpra/clients/elaine-179368'

This is with xpra 4.2.3-3.

Marking as critical because xpra does not run without this dependency installed.

Steps to reproduce:
1. Uninstall xorg-server on the remote, if installed.
2. Attempt to connect to a remote xpra server (-d ssh enabled for debugging):
xpra start ssh:user@host -d ssh --exit-with-children --start-child=xterm