Remove doc-validator workflow (#103504)

The tool is unmaintained. Most useful rules have been ported to Vale.

The remaining rules often exhibit false positives.

Signed-off-by: Jack Baldry <jack.baldry@grafana.com>

.github/workflows/doc-validator.yml

@@ -1,26 +0,0 @@
-name: "doc-validator"
-on:
-  workflow_dispatch:
-    inputs:
-      include:
-        description: |
-          Regular expression that matches paths to include in linting.
-
-          For example: docs/sources/(?:alerting|fundamentals)/.+\.md
-        required: true
-jobs:
-  doc-validator:
-    runs-on: "ubuntu-latest"
-    container:
-      image: "grafana/doc-validator:v5.2.0"
-    steps:
-      - name: "Checkout code"
-        uses: "actions/checkout@v4"
-      - name: "Run doc-validator tool"
-        # Only run doc-validator on specific directories.
-        run: >
-          doc-validator
-          '--include=${{ inputs.include }}'
-          '--skip-checks=^(?:image.+|canonical-does-not-match-pretty-URL)$'
-          ./docs/sources
-          /docs/grafana/latest