Clarify consistency regarding presence of elements at /collections and /collections/{collectionId}

[jerstlouis]

Clarify whether elements in /collections vs. in /collections/{collectionId} need to be consistent, but that an element being omitted from /collections but present /collections/{collectionId} still count as consistente.
This is different than Features where the interpretation is that if one is present at one location it needs to be in both.

[cmheazel]

Removed part C from Requirement 8.
API Common Part 2 now does not say anything about consistency between /collections and /collections/{collectionId} responses. All that is required is that they both comply with the requirements in the http://www.opengis.net/spec/ogcapi-common-2/1.0/rm/collection Requirements Module. This allows a SWG to use simplified representations of the /collections/{collectionId} response in the /collections response where appropriate.