Drop cgroup tests

We are no longer using cgroups in any special way in Apertis. In
addition it has been discovered that these tests have a flaw that allows
them to silently fail. Remove the tests as they are both broken and not
required.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

test-cases/cgroups-resource-control.yaml

-metadata:
-  name: cgroups-resource-control
-  format: "Apertis Test Definition 1.0"
-  image-types:
-    hmi:     [ armhf, arm64, amd64 ]
-    basesdk: [ amd64 ]
-    sdk:     [ amd64 ]
-  image-deployment:
-    - APT
-    - OSTree
-  group: "common"
-  type: functional
-  exec-type: automated
-  priority: medium
-  maintainer: "Apertis Project"
-  description: "Run cgroup resource control tests"
-
-  pre-conditions:
-    - "If running inside VirtualBox, disable the host I/O cache under \"storage\"
-       in the image settings. Not doing so can cause the test_blkio_* tests to
-       fail."
-
-  expected:
-    - "The output should be similar to that:"
-    - |
-        >>>> Test setup successfully!
-        >>> Running test 'test_cpu_shares' ... PASS
-        >>> Running test 'test_memory_limits' ... PASS
-        >>> Running test 'test_memory_threshold_notification' ... PASS
-        >>> Running test 'test_blkio_weights_random_read' ... PASS
-        >>> Running test 'test_blkio_weights_sequential_read' ... PASS
-        >>> Running test 'test_network_cgroup_priority_classification' ... PASS
-        >>> All tests PASSED successfully!
-    - "If any test failed, they will be listed instead of the success message:"
-    - |
-        >>>> The following tests FAILED:
-        [list of tests]
-
-install:
-  git-repos:
-    - url: https://gitlab.apertis.org/tests/cgroups-resource-control.git
-      branch: 'apertis/v2025dev2'
-
-run:
-  steps:
-    - "# Enter test directory:"
-    - cd cgroups-resource-control
-    - "# Execute the following commands:"
-    - common/run-test-in-systemd --name=cpu-shares --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_cpu_shares
-    - common/run-test-in-systemd --name=memory-limits --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_memory_limits
-    - common/run-test-in-systemd --name=memory-threshold-notification --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_memory_threshold_notification
-    - common/run-test-in-systemd --name=blkio-weights-random-read --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_blkio_weights_random_read
-    - common/run-test-in-systemd --name=blkio-weights-seq-read --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_blkio_weights_sequential_read
-    - common/run-test-in-systemd --name=network-cgroup-prio-class --timeout=900 env DEBUG=2 ./cgroups-resource-control.sh test_network_cgroup_priority_classification
-