[RFC] External FCC unlock scripts

This merge request drops the built-in automatic FCC unlock procedures for all modules.

If the user wants to keep on using the ModemManager-provided unlock procedures, they must manually install the suggested unlock scripts from /usr/share/ModemManager/fcc-unlock.d to /etc/ModemManager/fcc-unlock.d, make it root-owned, and update the file access mask to 0700. See https://modemmanager.org/docs/modemmanager/fcc-unlock

Alternatively, the user may also install a third party unlock tool provided by the laptop vendor or modem manufacturer itself.

The files installed under /etc/ModemManager/fcc-unlock.d should not be automatically removed on package upgrades, so this manual procedure would be a one-time operation.

Fixes #402 (closed)