ci: remove deepin 25 support

This partially reverts commit afcd126c00.

This fork do not need to preserve the support to deepin.
So I simply remove its CI.

.github/workflows/deepin.yml

@@ -1,35 +0,0 @@
-name: deepin 25 CI
-
-on: [push, pull_request, workflow_dispatch]
-
-jobs:
-  build-deepin-25-deb:
-    runs-on: ubuntu-latest
-    container:
-      image: linuxdeepin/deepin:crimson
-      options: --user root
-
-    steps:
-      - name: Update package lists and install basic tools
-        run: |
-          apt update
-          apt install -y git ca-certificates curl file
-      - uses: actions/checkout@v6
-      - name: Get build dept.
-        run: |
-          apt install -y cmake qt6-base-dev qt6-svg-dev qt6-tools-dev libexiv2-dev
-      - name: Build it
-        run: |
-          git config --global --add safe.directory '*' # to avoid "fatal: detected dubious ownership in repository at xxx"
-          cmake -Bbuild -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr .
-          cmake --build build -j
-          cd build
-          cpack -G DEB
-      - name: Try install it
-        run: |
-          cd build
-          apt install -y ./*.deb
-      - uses: actions/upload-artifact@v6
-        with:
-          name: deepin-25-deb-package
-          path: build/*.deb