Delete upstream workflows

This fork does not ship upstream's releases, and its hosted-runner jobs
never start here.

Claude-Session: https://claude.ai/code/session_01HuMDfgFssPUptYUzgZ6Cp8

.github/workflows/main.yml

@@ -1,67 +0,0 @@
-name: CI
-
-on: [push]
-
-jobs:
-  build-linux:
-
-    runs-on: ubuntu-latest
-
-    strategy:
-      matrix:
-        node-version: [10.x, 12.x, 14.x, 18.x, 20.x]
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v1
-      with:
-        node-version: ${{ matrix.node-version }}
-    - run: npm ci
-    - run: npm run build --if-present
-    - run: npm test
-    - run: npx standard
-      env:
-        CI: true
-
-  build-mac:
-
-    runs-on: macos-latest
-
-    strategy:
-      matrix:
-        node-version: [18.x, 20.x]
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v1
-      with:
-        node-version: ${{ matrix.node-version }}
-    - run: npm ci
-    - run: npm run build --if-present
-    - run: npm test
-    - run: npx standard
-      env:
-        CI: true
-
-  build-windows:
-
-    runs-on: windows-latest
-
-    strategy:
-      matrix:
-        node-version: [10.x, 12.x, 14.x, 18.x, 20.x]
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v1
-      with:
-        node-version: ${{ matrix.node-version }}
-    - run: npm ci
-    - run: npm run build --if-present
-    - run: npm test
-    - run: npx standard
-      env:
-        CI: true