Changes

debian/osmo-gbproxy.init: delete

Remove SysV init scripts. These are not really maintained anymore and
this makes it consistent with other Osmocom projects.

Avoids synchronizing with SysV scripts on debian:
  # systemctl enable osmo-gbproxy
  Synchronizing state of osmo-gbproxy.service with SysV service script with /usr/lib/systemd/systemd-sysv-install.
  Executing: /usr/lib/systemd/systemd-sysv-install enable osmo-gbproxy

Change-Id: I890b1ee9c201f09dcef968482c0bc5ed65ea7def