message: chore: remove a few unused deps
diff: "gcp-metadata": "^0.9.0",
  "google-auth-library": "^2.0.0",
  "google-gax": "^0.20.0",
  - "google-proto-files": "^0.17.0",
  "is": "^3.2.1",
  "lodash.merge": "^4.6.1",
  "on-finished": "^2.3.0",
  "nock": "^10.0.1",
  "nyc": "^13.0.1",
  "power-assert": "^1.6.0",
  - "propprop": "^0.3.1",
  "proxyquire": "^2.1.0",
  "typescript": "~3.1.0",
  "uuid": "^3.3.2"
  