Use session type to detect what to enable/disable

Parts of g-c-c use org.gtk.Settings.Purism is-phone gsetting to determine what to do. While this is o.k. to figure out docked mode it shouldn't be used to e.g. input restrictions or phosh features since that setting is only True in mobile mode, it's False when docked.

cc_panel_is_phosh () can be used for that (see !22 (merged)) instead. I'll fix up panels when they need other changes but let's have a bug.

/cc @mohammed.sadiq so this doesn't spread further.

The idea is certainly to make the conditional code blocks smaller and smaller.