Revert "tests: k8s: Allow passing rust-runtime env var to kata-deploy"

This reverts commit 44899d4cdf, as we've
decided to keep both golang and rust runtime installable and usable at
the same time.

The decision of having both runtimes installable and usable  will help
users to test and easily catch any possible differences between those
runtimes, helping us to get on par with both implementations.

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

.github/workflows/run-k8s-tests-on-aks.yaml

@@ -27,8 +27,6 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust-runtime:
-          - false
         host_os:
           - ubuntu
         vmm:
@@ -42,8 +40,6 @@ jobs:
         include:
           - host_os: cbl-mariner
             vmm: clh
-          - dragonball:
-            rust-runtime: true
     runs-on: ubuntu-latest
     env:
       DOCKER_REGISTRY: ${{ inputs.registry }}
@@ -55,7 +51,6 @@ jobs:
       KUBERNETES: "vanilla"
       USING_NFD: "false"
       K8S_TEST_HOST_TYPE: ${{ matrix.instance-type }}
-      RUST_RUNTIME: ${{ matrix.rust-runtime }}
     steps:
       - uses: actions/checkout@v4
         with: