Reduce the memory usage of a test

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@mstoykov, @robingustafsson - I'm directly merging this in master, to fix the build, but I intentionally doing it through a PR, so it'd be easier to reference in the future.
I'll create a new issue tomorrow that describes the things I've found out, but in short, the TestConsole test was taking over 1.2GB of RAM, and this fix dropped it back to 250-300 MB. We have some sort of memory sticking around when it should be garbage collected, and we probably have the same situation in other tests as well. Even worse, we might have something like this outside of the tests, in the actual k6 script execution... Hopefully not, but we should definitely investigate the root cause just in case.