Xpra: Ticket #2766: xdg menu data for macos shadow servers

See r26365.

Not sure it's very useful to provide a start menu for macos servers since those are shadow servers and we already see the desktop..

Sat, 23 Jan 2021 06:00:10 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2766