JS: Move all integration tests.

We no longer need the platform-specific directories, so simplify the test organization.
If you don't want this change, just skip merging this PR.
It's purely optional.

The PR also deletes a spurious qlpack.yml that I missed when converting the tests to pytest.

javascript/ql/integration-tests/diagnostics/internal-error/diagnostics.expected

@@ -0,0 +1,14 @@
+{
+  "markdownMessage": "Internal error: com.semmle.util.exception.CatastrophicError: The TypeScript parser wrapper crashed with exit code 1",
+  "severity": "unknown",
+  "source": {
+    "extractorName": "javascript",
+    "id": "js/internal-error",
+    "name": "Internal error"
+  },
+  "visibility": {
+    "cliSummaryTable": true,
+    "statusPage": false,
+    "telemetry": true
+  }
+}