Remove module shebangs

[ewels]

Script shebangs are not needed in modules, they're never directly executed. We only need them in Nextflow scripts that have an entry workflow (and to be honest, they're not really needed there either).

Removed from all modules and removed from the "Hello Nextflow" training material where modules are created.

Fixes #837

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[pinin4fjords]

I like shebangs as a cosmetic 'this is nextflow' sort of thing, but not enough to fight you on it.

[ewels]

I like shebangs as a cosmetic 'this is nextflow' sort of thing, but not enough to fight you on it.

That's actually how I explained their need when I recorded this last night - cosmetic, helping IDEs know which language syntax highlighting to use etc. But I didn't really buy the explanation myself 😅 Also, we don't use them in nf-core modules.

Mostly I found it was a bit of friction to repeatedly have to copy two things into a file instead of one, when the second part didn't make any practical difference.