quagga: remove watchquagga when start with systemd

When we start with sysvinit, watchquagga uses quagga init script to
monitor zebra daemon. But we need not do this in systemd environment.

Signed-off-by: Chong Lu <Chong.Lu@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>