Revert "Incorrect return type for SplFileObject::fgetcsv"

[VincentLanglet]

Reverts #464

Cf: #464 (comment)

[VincentLanglet]

Friendly ping @ondrejmirtes, is this PR ok ? :)

[ondrejmirtes]

Acording to your own comment (#464 (comment)), it can't return null without setFlags, i.e. this is a case for a type-specifying extension.

[VincentLanglet]

Hi @ondrejmirtes, by looking to the psalm issues, I discovered that null can be return without setFlags
See https://3v4l.org/Y7g3v or simplified https://3v4l.org/udltZ
So I don't think a type-specifying extension is the right way to do.

[VincentLanglet]

Friendly ping @ondrejmirtes

I think this PR should be preferred over a possibly type-specifying extension.

[ondrejmirtes]

Thank you!