package/systemd: remove SysV compatibility feature

package/systemd: remove SysV compatibility feature

Systemd enables compatibility with SysV services and utmp by default,
none of which is needed for buildroot as the packages' .mk will install
only the files for the chosen init system.

Furthermore, SysV support requires a setup where *both* /etc/init.d and
/etc/rc.d exists (the latter for the usual /etc/rcN.d). However, in
Buildroot, the latter does not exist; so we would not be able to provide
a working SysV support anyway.

So, just forcibly disable SysV support.

Signed-off-by: Norbert Lange <nolange79@gmail.com>
[yann.morin.1998@free.fr:
  - expand commit log
  - disable utmp in its own patch
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>