Remove GBL screenshots from Relations page

[rmseifried]

The OpenGeoMetadata documentation currently has a page that explains the various Relations fields and includes screenshots of the widgets as they appear in GeoBlacklight.

Issues:

1. With the changes to relationship widgets in GeoBlacklight v6 from Rework the relationships panel to add more context geoblacklight/geoblacklight#1917, these screenshots will be out-dated.
2. There is not currently versioning support on the OGM website, and it would add complication to maintain separate OGM documentation for how the schema works in GBL v4-5 vs GBL v6.
3. Some users of OGM Aardvark are not deploying the metadata in GeoBlacklight, so this explanation is irrelevant.

Proposal: Remove the GBL widget screenshots and explanation of how the metadata functions in GeoBlacklight, leaving just the basic explanation of how these fields work with each other within the metadata schema. Instead, move this content to the GeoBlacklight documentation site (see this issue).