Test: remove image_tests.sh

The image_tests.sh test case is being run only as part of the RHEL
nightly pipeline. This test case evolved over the years. In principle
it can do the following:
 1. Read test cases from /test/data/manifests.
 2. Rebuild the manifest attached to the test case directly by running
    osbuild.
 3. Compare the image-info report if attached to the test case (NOT
    done for any test cases in /test/data/manifests).
 4. Boot-test the built image in the respective environment (NOT done
    for any test cases in /test/data/manifests).

Moreover, these manifests (or test cases) are not updated regularly
after being generated for the first time.

All in all, given the fact that the test case rebuilds outdated
manifests by directly calling osbuild and does not run any additional
tests, it adds no value compared to the osbuild/images CI.
osbuild/images CI always rebuilds the latest image definition version
manifests with osbuild, so at the time the library is updated in
osbuild-composer, this scenario has already been tested.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

.gitlab-ci.yml

@@ -320,25 +320,6 @@ regression-no-explicit-rootfs-definition:
   variables:
     SCRIPT: regression-no-explicit-rootfs-definition.sh
 
-Image Tests:
-  stage: test
-  extends: .terraform
-  rules:
-    - !reference [.nightly_rules_all, rules]
-  script:
-    - schutzbot/deploy.sh
-    - /usr/libexec/tests/osbuild-composer/image_tests.sh
-  parallel:
-    matrix:
-      - RUNNER:
-          - aws/rhel-8.10-ga-x86_64
-          - aws/rhel-8.10-ga-aarch64
-          - aws/rhel-9.7-nightly-x86_64
-          - aws/rhel-9.7-nightly-aarch64
-          - aws/rhel-10.1-nightly-x86_64
-          - aws/rhel-10.1-nightly-aarch64
-        INTERNAL_NETWORK: ["true"]
-
 # NB (thozza): The rhel-edge-ci job is currently disabled because the tests have been consistently failing for a while.
 # The tests need to be investigated and fixed before re-enabling the job.
 # See https://issues.redhat.com/browse/HMS-8719