While preparing Tails 2.6 it was discovered that our last minute bump of
the 'debian' snapshot (to get Jessie 8.6) cause linux-compiler-gcc-* to
be updated to a version for another Linux version than what we install,
resulting in the tagged snapshot being impossible to create since it
would require two different linux source packages (which is not
supported).

This reverts commits:

* ab562fd4
* c0bc655c
* 80d0667a

The last minute attempt to include it in Tails 2.6 was a bad (too hasty)
idea, e.g. USB installations don't boot (pre-init results in
"FAT-fs (sdb1): IO charset ascii not found"). Also it seems that the
backport of Linux 4.7 hasn't gone through the proper Debian QA process.

We assume this name all over the place, so let's KISS.

As for why this renaming doesn't happen automatically any more (e.g. I
got vmlinuz-4.7.0-0.bpo.1-686), I can only guess. Perhaps it's the
non-standard linux flavor (686-unsigned) fed to live-config?

I suppose the signed one will the default (without any suffix), but it
is not available yet from Jessie backports.

It's worth noting that the linux-image-amd64 package is not satisfied by
the -unsigned packages yet, so we have to explicitly install the exact
image version we want.

While preparing Tails 2.6 it was discovered that our previous last
minute bump of the 'debian' snapshot (to get Jessie 8.6) caused
linux-compiler-gcc-4.9-x86 to be updated to a version from another Linux
source version (4.7) than what we planned to install (4.6), resulting in
the tagged snapshot being impossible to create since it would require
two different linux source packages which we do not support.

Note that this includes bumping the aufs4-standalone Git submodule to
the latest branch for Linux 4.7.

Conflicts:
	wiki/src/install/debian/usb.it.po
	wiki/src/install/inc/steps/create_persistence.inline.it.po
	wiki/src/install/inc/steps/download.inline.it.po
	wiki/src/install/inc/steps/restart_first_time.inline.it.po
	wiki/src/install/linux/usb.it.po
	wiki/src/install/mac/dvd.it.po
	wiki/src/install/mac/usb.it.po
	wiki/src/install/win/usb.it.po
	wiki/src/upgrade/tails.it.po

Fix-committed: #11372

Fix-committed: #11802

Will-fix: #11802

It actually doesn't seem to be necessary to suppress the annoying
"first run" prompt, but let's do it any way for consistency.

For the Tails 2.6 release, where we did a last minute bump of the
'debian' snapshot, some firmwares have suddenly been removed from
Debian Sid:

* firmware-amd-graphics
* firmware-intel-sound
* firmware-misc-nonfree

resulting in Tails not building any more.

Otherwise we'll have to wait for the bug and security fixes it has for
three months, until Tails 2.8. The one week delay of Tails 2.6 opened
the possibility for us to do this, so let's take the chance!

refs: #11507