Merge branch 'ab/retire-decl-of-missing-unused-funcs'

Remove external declaration of functions that no longer exist.

* ab/retire-decl-of-missing-unused-funcs:
  config.h: remove unused git_config_get_untracked_cache() declaration
  log-tree.h: remove unused function declarations
  grep.h: remove unused grep_threads_ok() declaration
  builtin.h: remove cmd_tar_tree() declaration

diff --cc config.h
Simple merge

diff --cc grep.h
Simple merge