ref: Cleanup deprecated method buildLocalBranch and proto field
The feature flag simplify_find_local_branches_response
has finished its rollout and this MR adds some missing cleanups.
- The method
buildLocalBranch
constructsFindLocalBranchResponse
, which is required byFindLocalBranchesResponse
and is no longer needed. - The
branches
field is actually deprecated and no longer referenced anymore
Part of #1294 (closed) and #4452 (closed)