Remove Ubuntu 22.04 CI/Docker infrastructure.

Ubuntu 24.04 is the most recent LTS release and it's 1.5 years old. We
definitely don't need 22.04 around.

Author: nnethercote

.github/workflows/ci_linux.yml

@@ -28,12 +28,6 @@ jobs:
       fail-fast: false
       matrix:
         variance:
-          - name: Ubuntu-22.04 / CUDA-12.8.1 / x86_64
-            image: "ghcr.io/rust-gpu/rust-cuda-ubuntu22-cuda12:latest"
-            runner: ubuntu-latest
-          - name: Ubuntu-22.04 / CUDA-12.8.1 / ARM64
-            image: "ghcr.io/rust-gpu/rust-cuda-ubuntu22-cuda12:latest"
-            runner: ubuntu-22.04-arm
           - name: Ubuntu-24.04 / CUDA-12.8.1 / x86_64
             image: "ghcr.io/rust-gpu/rust-cuda-ubuntu24-cuda12:latest"
             runner: ubuntu-latest
@@ -229,12 +223,6 @@ jobs:
       matrix:
         variance:
           # Must match the build job's matrix definition
-          - name: Ubuntu-22.04 / CUDA-12.8.1 / x86_64
-            image: "ghcr.io/rust-gpu/rust-cuda-ubuntu22-cuda12:latest"
-            runner: ubuntu-latest
-          - name: Ubuntu-22.04 / CUDA-12.8.1 / ARM64
-            image: "ghcr.io/rust-gpu/rust-cuda-ubuntu22-cuda12:latest"
-            runner: ubuntu-22.04-arm
           - name: Ubuntu-24.04 / CUDA-12.8.1 / x86_64
             image: "ghcr.io/rust-gpu/rust-cuda-ubuntu24-cuda12:latest"
             runner: ubuntu-latest

.github/workflows/container_images.yml

@@ -30,9 +30,6 @@ jobs:
           - runner: ubuntu-24.04-arm
             arch: arm64
         variance:
-          - name: Ubuntu-22.04/CUDA-12.8.1
-            image: "rust-gpu/rust-cuda-ubuntu22-cuda12"
-            dockerfile: ./container/ubuntu22-cuda12/Dockerfile
           - name: Ubuntu-24.04/CUDA-12.8.1
             image: "rust-gpu/rust-cuda-ubuntu24-cuda12"
             dockerfile: ./container/ubuntu24-cuda12/Dockerfile
@@ -154,8 +151,6 @@ jobs:
       fail-fast: false
       matrix:
         variance:
-          - name: Ubuntu-22.04/CUDA-12.8.1
-            image: "rust-gpu/rust-cuda-ubuntu22-cuda12"
           - name: Ubuntu-24.04/CUDA-12.8.1
             image: "rust-gpu/rust-cuda-ubuntu24-cuda12"
           - name: RockyLinux-9/CUDA-12.8.1