Remove re-use of IterationsResolver

This can be replaced with IterationsFinder

The following discussion from !47045 (merged) should be addressed:

• @alexkalderimis started a discussion: (+1 comment)

  Can we take this opportunity to remove the re-use of the iterations resolver here?

  I would like to move forwards with removing all re-use of resolvers from our code, and this will then be something we have to fix later.

  Really, this should just be a finder. I see from the test that this just calls the IterationsFinder, so that should be a simple change.

  Please see https://docs.gitlab.com/ee/development/api_graphql_styleguide.html#writing-resolvers