Merge branch 'jk/unused-parameter'

Merge branch 'jk/unused-parameter'

Mark-up unused parameters in the code so that we can eventually
enable -Wunused-parameter by default.

* jk/unused-parameter:
  t/helper: mark unused callback void data parameters
  tag: mark unused parameters in each_tag_name_fn callbacks
  rev-parse: mark unused parameter in for_each_abbrev callback
  replace: mark unused parameter in each_mergetag_fn callback
  replace: mark unused parameter in ref callback
  merge-tree: mark unused parameter in traverse callback
  fsck: mark unused parameters in various fsck callbacks
  revisions: drop unused "opt" parameter in "tweak" callbacks
  count-objects: mark unused parameter in alternates callback
  am: mark unused keep_cr parameters
  http-push: mark unused parameter in xml callback
  http: mark unused parameters in curl callbacks
  do_for_each_ref_helper(): mark unused repository parameter
  test-ref-store: drop unimplemented reflog-expire command