We've seen the following warning in CI jobs.
```
[DEPRECATED] The `--without` flag is deprecated because it relies on
being remembered across bundler invocations, which bundler will no
longer do in future versions. Instead please use `bundle config set
--local without 'system_tests'`, and stop using this flag
```
This updates the usage accordingly.
Change-Id: I9bddeea04ae0469b8074795b08f71ddd4ac6238e
6225d065c0