Changing auto-discovery URL to direct download URL

[emmambd]

What problem are we trying to solve?
We want to change the auto-discovery URL because "discovery" is not a commonly used term or convention in GTFS. (The original term was inspired by GBFS' systems.csv).

We intend to change this to "direct download URL" so it's clear that this link downloads a source.

How will we know when this is done?

All references to auto-discovery URL removed in the JSON schema, operations, and CSV export, and direct download URL used instead.

[e-lo]

I like the consolidation to a single URL to find the data - wondering if should just be URL? and then the description could be "URL which downloads the data".

[maximearmstrong]

@e-lo I saw your comment after merging the PR yesterday. The direct_download is nested under urls. We now have {"urls": {"direct_download": "...", "latest": "...", "license": "..."}}. Do you think that using URL instead of direct_download would be better in that context?