These were clearly missing!

cinnamon-regular package doesn't pull thunderbird in anymore,
so drop the l10n package too.

Looks like the initial empirical rule "mixin must not depend
on another mixin" is too restrictive for practical purposes
given enough image targets multiplied by enough platforms;
let's declare it obsolete and see what follows.

This reverts commit 147964b0.
installer-feature-create-ghost-directories not needed more.
See-also: https://bugzilla.altlinux.org/show_bug.cgi?id=37171

Not all systemd-based images need these settings,
so don't change +systemd alias.

See-also: https://lists.altlinux.org/pipermail/devel-distro/2019-July/001710.html

The builder-useradd package installs components of ALT build
environment into the system, namely gear, hasher, and git-core
required for those to work.

See commit 207cec89c4515fefa2b711acd06c645ed3bd0ee8.

KFLAVOURS can describe more than one kernel, get iterator back.

Fixes: 27674e29

- ppc64le support (glebfm@)
- build-vm hacked to build tarballs too (iv@ et al)
- p8.mk: dropped; along with other cleanups/fixups (antohami)

It was misleading already, and riscv64 is going to join the gang
(but not there yet) following aarch64, mipsel, ppc64le and more
e2k* subarches...

I've just borrowed glebfm@'s one introduced by commit
ec23a8ec before; this
still might be improved it seems.
Suggested-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>

When grub-install(1) works on non-virtualized PowerPC system it may
execute scripts from powerpc-utils package.

ieee1275boot bootloader support was added in mkimage 0.2.27.

Plymouth is (much more) portable, but our branding packages contain
bootsplash designs only on x86 nowdays.