Generate /etc/grml_live_version after FAI execution + drop /etc/dpkg/dpkg.cfg.d/unsaf...

Generate /etc/grml_live_version after FAI execution + drop /etc/dpkg/dpkg.cfg.d/unsafe-io code

FAI uses /etc to detect whether a chroot exists or not and will
skip debootstrap stage if /etc exists already. This causes serious
problems if the user doesn't have a BASEFILE, therefore we can't
edit files inside /etc before running FAI. :(

As a result:

1) generate /etc/grml_live_version *after* FAI has been executed

2) drop /etc/dpkg/dpkg.cfg.d/unsafe-io related code.
As stated in commit 9269536ba7bb7def8664972d153b71d193450595

| Enable --force-unsafe-io for dpkg
|
| While this might help on resource constrained systems, no performance
| impact has been measured during an unscientific test on a well-geared
| machine.

it does not seem to be that relevant. But even more important: it
doesn't work for systems without BASEFILEs because FAI skips the
debootstrap stage if /etc exists already, so we can't generate
/etc/dpkg/dpkg.cfg.d/unsafe-io *before* running FAI. Unless
someone comes up with benchmarks about real performance impacts
let's skip adding more fcopy logic...