Simplify startup and dependencies (#69)

Move file cleanups into a finish script for the service that created the
file (replace 02 / replace 03 commits)

Currently there is a whole dependency forest just to start a couple of
startup scripts in order.
Additionally all the services also have a dependency on all the startup
scripts.
This is unnecessary complex, simplify it:
- Move startup scripts to /etc/s6-overlay/startup.d
- oneshot service named "startup" from underlying image executes
all files in /etc/s6-overlay/startup.d in alphabetical order
- Remove various oneshot scripts from longrun service dependencies
Add "startup" oneshot service to longrun service dependencies

container-version is now being run by said startup script, remove the
double s6wrap prepending of an appropriate log name.

rootfs/etc/s6-overlay/s6-rc.d/mlat-client/finish

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec /etc/s6-overlay/scripts/mlat-client-finish

rootfs/etc/s6-overlay/s6-rc.d/readsb/finish

@@ -0,0 +1,2 @@
+#!/bin/sh
+exec /etc/s6-overlay/scripts/readsb-finish

rootfs/etc/s6-overlay/scripts/01-print-container-version → rootfs/etc/s6-overlay/startup.d/01-print-container-version

@@ -20,4 +20,4 @@ source /scripts/common
 # If not, see <https://www.gnu.org/licenses/>.
 #---------------------------------------------------------------------------------------------
 
-[[ -f /.CONTAINER_VERSION ]] && s6wrap --quiet --prepend=01-print-container-version --timestamps --args  echo "Container Version: $(cat /.CONTAINER_VERSION), build date $(stat -c '%y' /.CONTAINER_VERSION |sed 's|\(.*\)\.[0-9]* \(.*\)|\1 \2|g')" || true
+[[ -f /.CONTAINER_VERSION ]] && echo "Container Version: $(cat /.CONTAINER_VERSION), build date $(stat -c '%y' /.CONTAINER_VERSION |sed 's|\(.*\)\.[0-9]* \(.*\)|\1 \2|g')" || true