meta-agl-flutter: Simplify AGL integration

meta-agl-flutter: Simplify AGL integration

Changes:
- Remove Igalia homescreen and Pumped Fuel app recipes since they
  duplicate what is in meta-flutter.  Now that there is a AGL
  Flutter demo image in meta-agl, any recipes or bbappends for
  apps should go there except for the flutter-gallery integration
  for agl-image-flutter (see below).
- Move flutter-gallery systemd unit changes out of flutter-auto
  bbappend to a new flutter-gallery bbappend to simplify using
  flutter-auto on its own.  To facilitate interoperation with the
  use of flutter-gallery in the agl-ivi-demo-platform-flutter image,
  the systemd files are split out into a -init package that has been
  added to agl-image-flutter.
- Added back a reworked version of the app-id command-line option
  patch in the flutter-auto bbappend with the option changed to
  --xdg-shell-app-id per upstream request.  This wil be submitted
  upstream as time permits.  The merged patches that were deleted have
  been removed from SRC_URI.

The intent of the above is to move to meta-agl-flutter just having the
minimal set of changes to integrate flutter-auto with AGL use, with
the agl-image-flutter image kept as a simple smoketest / example.

Bug-AGL: SPEC-4485

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I171852820be404774d7580778643c801e8fad34f