Replace agl-demo* features with preconfigured images

Changes:
- Remove the agl-demo-preload and agl-demo-cluster-support setup
  features.
- Make the agl-weston-remoting setup feature a dependency of the
  agl-demo feature.  To accommodate this with respect to avoiding
  putting the remote-output display configuration into generated
  weston.ini files when not required, the logic for that has been
  moved from meta-agl-core's weston-ini-conf recipe, and extra
  weston-ini-conf-* packages with the remote output support enabled
  are now generated to be used in images when required.
- Add *-preconfigured versions of the images useful in a full demo
  setup (i.e. with "green machine" for tradeshows).  These images
  have the configuration tweaks that the build setup features
  enabled with conditional logic baked in.
- Remove now unnecessary connman-conf bbappend, we now assume that
  the IVI and cluster IP addresses are assigned as 192.168.10.2
  and 192.168.10.3 via DHCP in a full demo setup.

Notes:
- The cluster support in the *-preconfigured images assumes that
  the IVI board is at IP address 192.168.10.2, and both boards are
  in the 192.168.10.x subnet.

Bug-AGL: SPEC-5138

Change-Id: Icc472c6b602fa8fa5570af6cb0acaef853cbfa0f
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29866
ci-image-build: Jenkins Job builder account
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>