github: remove fcos-podman-next-build-prepush

It is flaking[1] from time to time on PRs and doesn't really add value
because noone is actually chaing the Containerfile. The task on main
that build a image based of main still exists as per Lokesh
podman-dekstop uses it for testing. In the near term we will get proper
builds in the podman-machine-os repo so this other workflow can
hopefully removed altogether.

[1] https://github.com/containers/podman/actions/runs/10618524888/job/29433963845?pr=23807

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

.github/workflows/fcos-podman-next-build-prepush-test.yml

@@ -1,31 +0,0 @@
-# This workflow only runs a build test to check for buildability issues before
-# PR merge. No registry push occurs here.
-name: Build FCOS image with podman-next
-
-on:
-  pull_request:
-    branches:
-      - main
-
-env:
-  IMAGE_NAME: fcos
-  IMAGE_REGISTRY: quay.io/podman
-  COPR_OWNER: rhcontainerbot
-  COPR_PROJECT: podman-next
-
-jobs:
-  fcos-podman-next-image-build-prepush-test:
-    runs-on: ubuntu-latest
-
-    steps:
-    - name: Check out code
-      uses: actions/checkout@v4
-
-    - name: Build FCOS Image
-      id: build_image_test
-      # Ref: https://github.com/redhat-actions/buildah-build
-      uses: redhat-actions/buildah-build@v2
-      with:
-        image: ${{ env.IMAGE_REGISTRY }}/${{ env.IMAGE_NAME }}
-        tags: ${{ github.sha }}
-        containerfiles: ./contrib/podman-next/fcos-podmanimage/Containerfile