Hide PIM entries in GNOME Shell and Disks

Originally created by @segfault on #16031 (Redmine)

Unlocking with a PIM is not supported by the cryptsetup version in Stretch, so we want to hide the PIM entries in our Stretch backports of the gnome-shell and gnome-disk-utility packages (see https://labs.riseup.net/code/issues/15927#note-5).

Feature Branch: feature/14481-TCRYPT-support-beta

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