Thanks to anonym!

This reverts commit feb938c7.

This reverts commit 46113506.

This breaks the test suite:

17:18:38  show origin/master:debian/changelog
17:18:38 + LAST_RELEASE_VERSION=3.11
17:18:38 + PREVIOUS_ISO=tails-amd64-3.11.iso
17:18:38 + wget --no-verbose https://iso-history.tails.boum.org/tails-amd64-3.11/tails-amd64-3.11.iso
17:18:38 Authentication selected: Basic realm="Tails :: ISO history"
17:18:38 https://iso-history.tails.boum.org/tails-amd64-3.11/tails-amd64-3.11.iso:
17:18:38 2018-11-27 17:18:38 ERROR 404: Not Found.

Re-use the same timestamp as the previous release to get an image very
close to the 3.10 one, hoping for diffoscope-ability.

This reverts commit 66efe503.

We did not do anything special to fix this problem so there's nothing to say
about it in the changelog. But it's user-visible so should probably mentioned in
the release notes.

The build of my first tentative 3.9~rc1 ISO failed with:

 E: Unable to locate package ^geoclue*
 E: Couldn't find any package by glob '^geoclue*'
 E: Couldn't find any package by regex '^geoclue*'
 E: config/chroot_local-hooks/98-remove_unwanted_packages failed (exit non-zero). You should check for errors.

That's because the partial, tagged APT snapshot used to build this ISO don't
include any package whose name matches ^geoclue. So let's only attempt to remove
such packages if at least one of them is installed.