SearchKit - remove extra irrelevant fields from bridge joins

[colemanw]

Overview

Removes a few confusingly redundant fields from searchKit when using a bridge join.

Before

Search for: Contacts
With: Related Contacts
Where: (notice that contact A display name and contact B display names are options in the list)

After

Redundant options gone

Technical Details

Those fields are redundant and would have caused unnecessary extra joins to be added to the query.

[civibot]

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[eileenmcnaughton]

OK - I can see that there are 4 display name variants without this & 2 with it - so makes sense