Remove explorer preview workflow (#28154)

.github/workflows/explorer_preview.yml

@@ -1,58 +0,0 @@
-name : explorer_preview
-on:
-  workflow_run:
-    workflows: ["Explorer_build&test_on_PR"]
-    types: 
-      - completed
-jobs:
-   explorer_preview:
-    runs-on: ubuntu-latest
-    if: ${{ github.event.workflow_run.conclusion == 'success' }}
-    steps:
-      - uses: actions/checkout@v2
-        with:
-          ref: ${{ github.event.pull_request.head.sha }}
-      - uses: amondnet/vercel-action@v20
-        with:
-          vercel-token: ${{ secrets.VERCEL_TOKEN }} # Required
-          github-token: ${{ secrets.GITHUB_TOKEN }} #Optional 
-          vercel-org-id: ${{ secrets.ORG_ID}}  #Required
-          vercel-project-id: ${{ secrets.PROJECT_ID}} #Required
-          scope: ${{ secrets.TEAM_ID }}
-     
-      - name: vercel url
-        run : |
-              touch vercelfile.txt
-              vercel --token ${{secrets.VERCEL_TOKEN}}  ls explorer --scope team_8A2WD7p4uR7tmKX9M68loHXI > vercelfile.txt
-              touch vercelfile1.txt
-              head -n 2 vercelfile.txt > vercelfile1.txt
-              touch vercelfile2.txt
-              tail -n 1 vercelfile1.txt > vercelfile2.txt
-              filtered_url7=$(cut -f7 -d" " vercelfile2.txt)
-              echo "filtered_url7 is: $filtered_url7" 
-              touch .env.preview1
-              echo "$filtered_url7" > .env.preview1
-              #filtered_url=$(cat vercelfile2.txt )
-              #echo "$filtered_url" >> .env.preview1 
-
-      - name: Fetching Vercel Preview Deployment Link
-        uses: mathiasvr/command-output@v1
-        id: test1
-        with:
-          run: |
-               echo "$(cat .env.preview1)"
-      - name: Fetching PR commit URL
-        uses: mathiasvr/command-output@v1
-        id: test2
-        with:
-          run: |
-               HEAD_SHA=$(curl -H "Accept: application/vnd.github.v3+json"  https://api.github.com/repos/solana-labs/solana/pulls | jq .[0] | jq -r .head.sha)
-               USER_NAME=$(curl -H "Accept: application/vnd.github.v3+json"  https://api.github.com/repos/solana-labs/solana/pulls | jq .[0] | jq -r .head.user.login)
-               echo "github.com/$USER_NAME/solana/commit/$HEAD_SHA"
-      
-      - name: Slack Notification4
-        uses: rtCamp/action-slack-notify@master
-        env:
-         SLACK_MESSAGE: ' Vercel Link: ${{ steps.test1.outputs.stdout }} PR Commit: ${{steps.test2.outputs.stdout}}'
-         SLACK_TITLE: Vercel "Explorer" Preview Deployment Link , PR Commit
-         SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }}