So there's no chance it will try to use the Torified DNS server, in
case our firewall fails.

It makes a bit of sense on its own, and it guarantees that no weird
cruft in ~/.tor-browser will interfere for whatever reason.

No code is deleted/added/modified, only moved.

This way the chroot browsers will close faster.

We could use `cp --no-dereference` before, when the TBB_EXT dir only
contained symlinks. This will reduce the memory footprint of the
chroot browsers, and incidentally fixed a bug where the
unsafe-browser's name wasn't set since we copied the langpack before
we fix the name in it.

Apparently the name is dictated completely by Torbutton, so
set_chroot_torbutton_browser_name() is enough. This should speed up
the start and reduce the memory footprint.

We don't have to any more (after the TBB migration) since we
explicitly set up the ones we want to use. This should speed up the
start and reduce the memory footprint.

We don't have to fix the name in all branding files, only for the
locale we're actually gonna use.

And use it consistently in all places instead of using the value as a
magic constant.