Some future side-effect could cause unexpected behavior if applied
twice.

When trying to build Tails 2.9 with:

    TAILS_BUILD_OPTIONS="cleanall defaultcomp ram"

set, the resulting `options` string contained:

    "[...] ramcleanall [...]"

which is really bad. Fixup on this commit:

    4e8410a8 Enforce `cleanall` when building a release.

Fix-committed: #12029

Will-fix: #12029

Fix-committed: #11913

Fix-committed: #12028

This reverts commit 8c4879ea.

That change broke the "The Unsafe Browser can be used in all languages
supported in Tails" scenario because the vi_VI locale doesn't
exist. Let's solve this properly...

Merge remote-tracking branch 'origin/test/11901-mat-does-not-clean-PDF-anymore' into stable (Fix-committed: #11901)

Merge remote-tracking branch 'origin/bugfix/11965-virtualbox-5.1.8' into stable (Fix-committed: #11965)

I.e. the tests are done using a tool *different* from MAT, the tool
being tested here.

Refs: #11901

Because MAT doesn't clean PDFs anymore. :_(

Will-fix: #11901

If we have uploaded a package there we likely want it to be installable
no matter which such label it has.

Will-fix: #11965

Otherwise they are only removed from Enlgish locales. Note that the
langpacks contain copies of the English plugins, not localized versions,
so we actually do not lose nothing.

Without   the '6.' is considered as the start of a list and the
following line of code is not formatted as code.

This reverts commit 6d9e5eaf.

We are generating our own DDG plugin now, so it won't be present in
omni.ja. And even if we didn't we'll, soon ship a Tor Browser where this
fix is already present.

At least VI is what DDG expects, not VN. For spellchecking VN is
expected, but we'll try the short locale too which will work.

Refs: #11913