Merge branch 'jk/ort-unused-parameter-cleanups'

Code clean-up.

* jk/ort-unused-parameter-cleanups:
  merge-ort: lowercase a few error messages
  merge-ort: drop unused "opt" parameter from merge_check_renames_reusable()
  merge-ort: drop unused parameters from detect_and_process_renames()
  merge-ort: stop passing "opt" to read_oid_strbuf()
  merge-ort: drop custom err() function