procmail is listed with packages said to be “Priority: standard” but
it's only “Priority: optional” in stretch. With monkeysphere going away
(in 2cee7949), this package is no longer
pull and no longer visible in tagged snapshots, which leads to this
FTBFS:

    E: Unable to locate package procmail
    E: config/chroot_local-hooks/98-remove_unwanted_packages failed (exit non-zero). You should check for errors.

Hotfix for 3.14: switch to mutt-style removal, and trigger a purge for
procmail only if it's (known and) installed.

I'm tempted to remove it altogether but I'm too lazy to create
a branch for this now.

Merge remote-tracking branch 'origin/bugfix/16602-parts-of-unlock-veracrypt-volumes-not-translated' into stable (Fix-committed: #16602)

To be consistent with other Tails apps (e.g. additional-software).

Merge branch 'bugfix/16720-linux-4.19.37-nosmt+force-all-tests' into stable (Fix-committed: #16720, #16708)

Enable all available mitigations for the MDS vulnerability and disable SMT on vulnerable CPUs (refs: #16720)

Its only purpose is to depend on firmware-linux-free and firmware-linux-nonfree,
which we explicitly install all these packages already. As per the previous
commit, we can't install firmware-linux-nonfree at the moment, so in turn we
can't install firmware-linux.

Its only purpose is to depend on firmware-misc-nonfree and
firmware-amd-graphics, and to recommend intel-microcode and amd64-microcode.
We explicitly install all these packages already. The dependency is versioned
which breaks our build at the moment, since we want to ship a different
version of firmware-amd-graphics (4fbcc2a1).

The version in sid now displays a warning and exits, while 3.2.3-1 is still
usable, in the rare cases when it manages to connect to the network, despite
being affected by problematic phishing attacks which will only be solved once
the package in Debian is updated to a newer upstream version.

… i.e. currently 20190114-1~bpo9+2, which is similar to 20190114-1
that we've shipped in Tails 3.13.2.

Rationale: avoid shipping the https://bugs.debian.org/928631 regression.