Merge branch 'jk/fetch-ref-prefix-cleanup' into tb/refspec-fetch-cleanup

Merge branch 'jk/fetch-ref-prefix-cleanup' into tb/refspec-fetch-cleanup

* jk/fetch-ref-prefix-cleanup:
  fetch: use ref prefix list to skip ls-refs
  fetch: avoid ls-refs only to ask for HEAD symref update
  fetch: stop protecting additions to ref-prefix list
  fetch: ask server to advertise HEAD for config-less fetch
  refspec_ref_prefixes(): clean up refspec_item logic
  t5516: beef up exact-oid ref prefixes test
  t5516: drop NEEDSWORK about v2 reachability behavior
  t5516: prefer "oid" to "sha1" in some test titles
  t5702: fix typo in test name