Remove triage automation

The triage board isn't being used, so no reason to have automation (it's also old style and should be modernised if there's interest in using it again)

.github/workflows/triage-incoming.yaml

@@ -1,27 +0,0 @@
-name: Move new issues into triage board
-
-on:
-  issues:
-    types: [opened]
-
-jobs:
-  add-to-project:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: octokit/graphql-action@v2.x
-        id: add_to_project
-        with:
-          headers: '{"GraphQL-Features": "projects_next_graphql"}'
-          query: |
-            mutation add_to_project($projectid:ID!,$contentid:ID!) {
-              addProjectV2ItemById(input: {projectId: $projectid contentId: $contentid}) {
-                item {
-                  id
-                }
-              }
-            }
-          projectid: ${{ env.PROJECT_ID }}
-          contentid: ${{ github.event.issue.node_id }}
-        env:
-          PROJECT_ID: "PVT_kwDOAM0swc4AH1sa"
-          GITHUB_TOKEN: ${{ secrets.ELEMENT_BOT_TOKEN }}