Merge branch 'kn/refs-optim-cleanup'

Code clean-up.

* kn/refs-optim-cleanup:
  t/pack-refs-tests: move the 'test_done' to callees
  refs: rename 'pack_refs_opts' to 'refs_optimize_opts'
  refs: move to using the '.optimize' functions

diff --cc refs/debug.c
Simple merge

diff --cc refs/files-backend.c
Simple merge

diff --cc refs/reftable-backend.c
Simple merge