Install ts-unused-exports

Author: robertbrignull

extensions/ql-vscode/package-lock.json

@@ -1882,6 +1882,7 @@
     "ts-loader": "^9.4.2",
     "ts-node": "^10.7.0",
     "ts-protoc-gen": "^0.9.0",
+    "ts-unused-exports": "^9.0.5",
     "typescript": "^5.0.2",
     "webpack": "^5.76.0",
     "webpack-cli": "^5.0.1"