Deprecate nogui: in qrexec

[DemiMarie]

How to file a helpful issue

The problem you're addressing (if any)

nogui: in qrexec command lines modifies the execution environment of the service. However, as per @marmarek, the service execution environment is the responsibility of the VM, not of the way the service is called. Furthermore, nogui: cannot be selected in policy files.

The solution you'd like

Deprecate nogui: and eventually get rid of it entirely. This also means deprecating qvm-run --service --no-gui. qvm-run --no-gui without --service would still be allowed, as it would work by changing the service that gets called.

The value to a user, and who that user might be

This will remove a confusing part of the qrexec system that can misbehave in confusing ways.

Completion criteria checklist

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