Revert "CI: add super-linter for pull requests"

Initial motivation for this commit was 'Just merge and see how people like it?'
https://github.com/openwrt/packages/pull/13358#issuecomment-692309158

It seems that many contributors don't like it.
https://github.com/openwrt/packages/issues/13395

So this should be reverted until issues with the linter can be
resolved.

This reverts commit 2b5de22202.

.github/workflows/linter.yml

@@ -1,22 +0,0 @@
-name: Lint Pull Request
-
-# Documentation:
-# https://github.com/github/super-linter
- 
-on:
-  pull_request:
-    branches: [master]
-jobs:
-  build:
-    name: Lint Code Base
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout Code
-        uses: actions/checkout@v2
-
-      - name: Lint Code Base
-        uses: github/super-linter@v3
-        env:
-          VALIDATE_ALL_CODEBASE: false
-          DEFAULT_BRANCH: master
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}