Cleaning up redundant packages/config bits

Using the Buster opportunity for some spring cleaning in the stuff copied into rootfs from /volumio folder in the repo.

In #413 I only looked into the <device>config.sh and <device>image.sh bits, and kept the volumioconfig.sh and configure.sh parts.

From a quick exploration, here are some things to look at

Services

These are just copied into the rootfs, but never used

[ ] volumiosplash.service
[ ] xbindkeysrc.service

Irrelevant/Redundant configuration (?)

Not sure if these are still required?

[ ] /etc/hostapd/hostapd.conf (not copied, and we append anyway in volumioconfig.sh to probably the default config?)
[ ] /etc/inittab
[ ] /etc/netplug/*
[ ] /etc/hosts
[ ] /etc/nsswitch.conf Why is the default configuration overwritten? Do we need this?

Stuff that is handled by Node back end?

[ ] mpd.conf which is overwritten by mpd.conf.tmpl
[ ] /etc/shairport-sync.conf copied in by configure.sh but overridden by /tmp/shairport-sync.conf in shairport-sync.service

Things that are probably redundant?

[ ] /etc/network/if-pre-up.d/powersavedisable vs /bin/wifistart.sh -- probably required for the udev network interface renaming rules?
[ ] /etc/iptables.rules vs iptables.service

Packages

We should probably also evaluating packages that are included in the next round.. djmount - file system client for mounting network media servers netplug - network link monitor daemon -- (switched to ifplugd d6c23e8) udisks, udisks-glue and accompanying configuration bits that are now managed directly using node-udev dhcpcd/isc-dhcp-server/hotspot.sh stuff that can be achieved with dnsmasq (implemented in buster, and probably needs more testing)

I'd like to make a bit more radical suggestion -- instead of re-looking at things here, we start fresh with buster, and carefully select things that are still required? The main architects/contributors (@gkkpch @macmpi @xipmix @volumio of the top of my head) should then review what gets added. Thoughts?

volumio / Build