Remove System V init support

- Make systemd the only supported init system by removing System V init
  and insserv references
- Ensure package builds with no init system dependencies if built
  without systemd (for example for use in containers)
- Apply some spec-cleaner suggestions (update copyright year, sort
  requirements, adjust spacing)

Signed-off-by: Georg Pfuetzenreuter <[email protected]>

Author: tacerus