refactor: drop repo-tool as an exec wrapper (#61)

Author: JustinBeckwith

monitoring/snippets/package.json

@@ -9,7 +9,7 @@
     "node": ">=4.0.0"
   },
   "scripts": {
-    "test": "repo-tools test run --cmd ava -- -T 3m --verbose system-test/*.test.js"
+    "test": "ava -T 3m --verbose system-test/*.test.js"
   },
   "dependencies": {
     "@google-cloud/monitoring": "0.5.0",