search: simplify repo allow list computation
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/32708.
Another removal of query.Fields()
Test plan
Semantics-preserving.
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/32708.
Another removal of query.Fields()
Semantics-preserving.