Clean up test files

[bkamins]

In this PR I fix the indentation in test files to follow standard Julia recommendations.
That is: I removed indentation of code inside module clause.
The reason is that:

1. sometimes we did it and sometimes we did not do it
2. these 4 spaces sometimes matter for longer expressions when I want to avoid wrapping

@nalimilan I would also remove files test/stdin.sh and test/data/iris.csv as I think they are not used anywhere (but I might have missed something).

[nalimilan]

Feel free to remove said files.

[bkamins]

Squashed. This will require all open PRs to be rebased, but it was uavoidable and rebasing should be simple.