De-duplicate questions with multiple listeners

When multiple listeners are registered for a resolve query, they were
duplicated in servicesToResolve, so the A/AAAA/PTR/SRV queries would
appear multiple times in the question section of query packets.

Ensure that makeResponsesForResolve does not generate duplicate
responses for duplicate listeners to avoid the duplicate queries.

Bug: 288174267
Fixes: 285090822
Test: atest
Change-Id: Ie6f76de6bfc5018c4c479505f99fbe6d81b64434