chore: Remove merge-to-downstream (#6741)

.github/workflows/trigger-merge-to-downstream.yml

@@ -1,24 +0,0 @@
-name: trigger-merge-to-downstream
-
-on:
-  push:
-    branches:
-      - main
-      - release/**
-
-permissions:
-  contents: read
-
-jobs:
-  trigger-merge:
-    if: github.repository == 'hashicorp/boundary'
-    runs-on: ${{ fromJSON(vars.RUNNER) }}
-    env:
-      DOWNSTREAM_SLUG: ${{ vars.DOWNSTREAM_SLUG }}
-      DOWNSTREAM_TOK: ${{ secrets.DOWNSTREAM_TOK }}
-      DOWNSTREAM_WORKFLOW: ${{ vars.DOWNSTREAM_WORKFLOW }}
-    steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-      - name: Trigger Merge
-        run: |
-          ./scripts/trigger-merge-to-downstream-gha ${{ github.ref_name }}