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