Remove dependency on @google-cloud/common (#165)

Author: JustinBeckwith

packages/google-cloud-dialogflow/package.json

@@ -56,7 +56,6 @@
     "protobufjs": "^6.8.0"
   },
   "devDependencies": {
-    "@google-cloud/common": "^0.20.0",
     "@google-cloud/nodejs-repo-tools": "^2.1.1",
     "async": "^2.6.0",
     "codecov": "^3.0.0",

packages/google-cloud-dialogflow/samples/package.json

@@ -12,7 +12,6 @@
     "test": "ava system-test"
   },
   "dependencies": {
-    "@google-cloud/common": "^0.20.0",
     "dialogflow": "0.6.0",
     "grpc": "^1.4.1",
     "pump": "^3.0.0",