fix: Delete obsolete platform-compatibility-test (#2419)

Closes: #2418 
Refs: #2417 #1308 

## Description

Adapted from
#2419 (review)
below

The platform compatibility test specifically validates that SES works on
Node.js 12 and can be deleted since it has vanished into history.
Node.js 12 required special consideration because of its experimental
ESM support. Delete the `test:platform-compatibility` script in the ses
`package.json`, as well as the `test/package` fixture in ci.yml

Immediate motivation explained in #2418 , #2417 broken the
platform-compatibility-test tests because it depends on the platform
providing either `Array.prototype.transfer` or `structuredClone`. Node
supports `transfer` starting with Node 22, but supports
`structuredClone` starting in Node 18. That should be fine, since that
is our declared support floor. This PR changes our one known remaining
dependence on Node 12.

### Security Considerations

none
### Scaling Considerations

none
### Documentation Considerations

none beyond the need to explain our platform requirements, which this PR
does not change.
### Testing Considerations

The point. This PR only affects tests, not production code.

Reviewers, should this PR be labeled `test:` instead of `fix:`?

### Compatibility and Upgrade Considerations

After this PR, we will no longer notice further breakage on Node < 18.
That fits with our declared support floor.

.github/workflows/ci.yml

@@ -231,57 +231,6 @@ jobs:
       - name: Run yarn test262
         run: exit 0 # TODO remove test262 from required tests for CI
 
-  platform-compatibility-test:
-    name: platform-compatibility-test
-
-    # begin macro
-
-    runs-on: ${{ matrix.platform }}
-    strategy:
-      fail-fast: false
-      matrix:
-        node-version: [18.x, 20.x]
-        platform: [ubuntu-latest]
-
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-
-      # without this, setup-node errors on mismatched yarn versions
-      - run: corepack enable
-
-      - name: Use Node.js ${{ matrix.node-version }}
-        uses: actions/setup-node@v3
-        with:
-          node-version: ${{ matrix.node-version }}
-          cache: yarn
-
-      - name: Echo node version
-        run: node --version
-
-      - name: Install dependencies
-        run: yarn install --immutable
-
-      # end macro
-
-      - name: 'build'
-        run: yarn run build
-
-      # fails under Node v12
-      - run: corepack disable
-
-      - name: 'switch to node v12'
-        uses: actions/setup-node@v3
-        with:
-          node-version: '12.x'
-
-      - name: Echo node version
-        run: node --version
-
-      - name: Run test:platform-compatibility
-        # npm b/c Yarn 4 doesn't work in Node 12
-        run: cd packages/ses && npm run test:platform-compatibility
-
   viable-release:
     name: viable-release
 

packages/ses/package.json

@@ -72,8 +72,7 @@
     "lint:types": "tsc",
     "prepare": "npm run clean && npm run build",
     "qt": "ava",
-    "test": "tsd && ava",
-    "test:platform-compatibility": "node test/package/test.cjs"
+    "test": "tsd && ava"
   },
   "dependencies": {
     "@endo/env-options": "workspace:^"