chore: use es classes in a few places (#297)

Author: JustinBeckwith

handwritten/spanner/.gitignore

@@ -12,3 +12,5 @@ system-test/*key.json
 google-cloud-logging-winston-*.tgz
 google-cloud-logging-bunyan-*.tgz
 package-lock.json
+.vscode
+yarn.lock

handwritten/spanner/package.json

@@ -80,7 +80,6 @@
     "lodash.merge": "^4.6.1",
     "lodash.snakecase": "^4.1.1",
     "merge-stream": "^1.0.1",
-    "modelo": "^4.2.3",
     "p-queue": "^2.4.2",
     "protobufjs": "^6.8.6",
     "split-array-stream": "^2.0.0",