[CI] Remove redundant trigger-review-pipeline job (#13547)

This job is now redundant since pipelines are run for each commit, so it can be safely removed. Cheers

substrate/.github/workflows/trigger-review-pipeline.yml

-name: Trigger pipeline for review
-
-on:
-  pull_request:
-    types: [ready_for_review]
-
-jobs:
-  trigger:
-    runs-on: ubuntu-latest
-
-    steps:
-      - name: Trigger pipeline
-        run: |
-          curl -X POST \
-            -F token="$TOKEN" \
-            -F ref="$REF" \
-            https://gitlab.parity.io/api/v4/projects/145/trigger/pipeline
-        env:
-          REF: ${{ github.event.number }}
-          TOKEN: ${{ secrets.GITLAB_TRIGGER_TOKEN }}