disable qubes-icon-sender on sys-net and sys-usb

[Guiiix]

Qubes icon sender allows to update applications windows icons. In practice, few windows are opened on the sys-vms. Disabling this service allows to recover some RAM without causing inconvenience.

[marmarek]

PipelineRetry

[ben-grande]

Took me a minute but for others that are reading and trying to understand why Exec=/usr/lib/qubes/qvm-service-wrapper program was not used instead, it is because qubes-icon-sender is not in $PATH so can't use basename which is necessary for the detection of /run/qubes-service/$service to work. Naming the service qubes-icon-sender and enabling by default in Qubes could be another solution, but as I see the minimal-(netvm|usbvm) being used elsewhere, I understand the reasoning now.