Implement or delete converter stub from old-style BIDS schema spec to current spec

[happy5214]

The convertOldSpecToSchemasSpec function was left unimplemented when support for the current BIDS HED schema specification model was released. It was intended to map the originally proposed format (see hed-standard/hed-specification#156) to the approved spec. Two questions:

1. Does anyone still use the originally proposed model for specifying HED schema versions?
2. Does this function still need to exist?

CC @VisLab

[VisLab]

@happy5214 We're going to have to go through this together as I am not sure of the exact differences. We'll have to evaluate.

[VisLab]

This only appeared in a prerelease and was replaced by the current specification upon review by the HED Working Group.