Clean up APT preferences post-migration to Tor Browser
Originally created by @intrigeri on #8470 (Redmine)
We still have APT pinning for e.g. xul-ext-https-everywhere and xul-ext-noscript, that we don’t ship anymore from Debian packages (but instead using the copy from the Tor Browser).
Feature Branch: bugfix/8470-clean-up-apt-pinning