GHA: drop linter

It never worked on this stable branch and we don't maintain it, so
it just adds noise, drop it

.github/workflows/linter.yml

@@ -1,44 +0,0 @@
----
-# vi: ts=2 sw=2 et:
-# SPDX-License-Identifier: LGPL-2.1-or-later
-# https://github.com/marketplace/actions/super-linter
-name: Lint Code Base
-
-on:
-  pull_request:
-    branches:
-      - main
-      - v[0-9]+-stable
-
-permissions:
-  contents: read
-
-jobs:
-  build:
-    name: Lint Code Base
-    runs-on: ubuntu-latest
-    concurrency:
-      group: ${{ github.workflow }}-${{ github.ref }}
-      cancel-in-progress: true
-
-    steps:
-      - name: Repo checkout
-        uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b
-        with:
-          # We need a full repo clone
-          fetch-depth: 0
-
-      - name: Lint Code Base
-        uses: github/super-linter/slim@454ba4482ce2cd0c505bc592e83c06e1e37ade61
-        env:
-          DEFAULT_BRANCH: main
-          MULTI_STATUS: false
-          # Excludes:
-          #   - man/.* - all snippets in man pages (false positives due to
-          #              missing shebangs)
-          #   - .*\.(in|SKELETON) - all template/skeleton files
-          #                         except kernel-install
-          FILTER_REGEX_EXCLUDE: .*/(man/.*|([^k]|k(k|ek)*([^ek]|e[^kr]))*(k(k|ek)*e?)?\.(in|SKELETON))$
-          VALIDATE_ALL_CODEBASE: false
-          VALIDATE_BASH: true
-          VALIDATE_GITHUB_ACTIONS: true