test/data/manifests: avoid duplicate booting

We have integration tests that boot most of the image types, let
the image tests focus on the actual content of the images, shaving
off considerable CI time.

The only missing one is OpenStack (which should be ported over) and
tar (which we need to define the integration test for).

Signed-off-by: Tom Gundersen <teg@jklm.no>

test/data/manifests/rhel_8-ppc64le-qcow2-boot.json

@@ -1,7 +1,4 @@
 {
-  "boot": {
-    "type": "qemu"
-  },
   "compose-request": {
     "distro": "rhel-8",
     "arch": "ppc64le",