Persistence-setup: stop depending on synaptic

tails-persistence-setup depends on synaptic to use one of its icons. That should be fixed as part of this ticket, for instance using package-x-generic or/and x-package-repository icons provided by gnome-icon-theme.

Feature Branch: persistence-setup.git:bugfix/15263-stop-depend-on-synaptic,persistence-setup.git:debian_bugfix/15263-stop-depend-on-synaptic

Parent Task: #15262

Original created by @alant on 15263 (Redmine)

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