Update schema id URL from NABSA to MobilityData repo

[richfab]

• The schema $id URLs should be updated from NABSA to MobilityData repo.

Example in https://github.com/MobilityData/gbfs-json-schema/blob/master/v3.0-RC/gbfs.json#L3:

Before	After
"$id": "https://github.com/NABSA/gbfs/blob/v3.0-RC/gbfs.md#gbfsjson"	"$id": "https://github.com/MobilityData/gbfs/blob/v3.0-RC/gbfs.md#gbfsjson"

• At the same time, we should remove the release annotations from the URLs as they break the anchor.

Example in https://github.com/MobilityData/gbfs-json-schema/blob/master/v3.0-RC/vehicle_types.json#L4:

Before	After
"$id": "https://github.com/NABSA/gbfs/blob/v3.0-RC/gbfs.md#vehicle_typesjson-added-in-v21-rc",	"$id": "https://github.com/NABSA/gbfs/blob/v3.0-RC/gbfs.md#vehicle_typesjson"-added-in-v21-rc,

• The $id URLs also need to be updated in the gbfs-validator (eg: https://github.com/MobilityData/gbfs-validator/blob/master/gbfs-validator/versions/partials/v3.0-RC2/station_status/required_vehicle_types_available.js#L7)

Before	After
$ref: 'https://github.com/NABSA/gbfs/blob/v3.0-RC2/gbfs.md#station_statusjson'	$ref: 'https://github.com/MobilityData/gbfs/blob/v3.0-RC2/gbfs.md#station_statusjson'