"phenotype.tsv" referenced in part of validator, but this is not a BIDS file

[sappelhoff]

https://github.com/bids-standard/bids-validator/blob/2d923f501bcf97b14e612833fb1bcb3af39f2b67/bids-validator/bids_validator/tsv/non_custom_columns.json#L68

In BIDS we have phenotype/<whatever-name>.tsv but not phenotype.tsv. See: https://bids-specification.readthedocs.io/en/stable/modality-agnostic-files.html#phenotypic-and-assessment-data

brought up by @VisLab in #1876

[effigies]

I'm not sure if this line was ever used to implement any tests. It could be vestigial.