Drop the appstream validation ci

for historical reasons this flatpak has an appid that is considered
invalid because of capitalization so the validation would always fail.

.github/workflows/main.yml

@@ -1,20 +0,0 @@
-name: CI
-on:
-  push:
-  # Allows you to run this workflow manually from the Actions tab
-  workflow_dispatch:
-
-jobs:
-  appstream-validate:
-    runs-on: ubuntu-24.04
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Install appstream
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y appstream
-
-      - name: Validate metainfo
-        run: |
-          appstreamcli validate --strict --pedantic --explain org.DolphinEmu.dolphin-emu.metainfo.xml