travis: Stop using --with-init-script

We're gonna drop support for non-systemd init scripts soon,
and we don't want Travis CI builds to break when we do.

Since we have init system auto-detection, we can just rely on
that and stop passing --with-init-script to configure entirely.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

.travis.yml

@@ -11,13 +11,11 @@ matrix:
         - docker
       env:
         - IMAGE="ubuntu-18"
-        - DISTCHECK_CONFIGURE_FLAGS="--with-init-script=systemd"
         - DOCKER_CMD="$LINUX_CMD"
     - services:
         - docker
       env:
         - IMAGE="centos-7"
-        - DISTCHECK_CONFIGURE_FLAGS="--with-init-script=upstart"
         - DOCKER_CMD="$LINUX_CMD"
     - services:
         - docker