Add flist_find_ignore_dirness() and change delete_in_dir() to use it.

This fixes an issue with -K noticed by eric casteleijn, avoids some
inconsistent itemizing when a file/dir is replaced by a dir/file,
and removes a now-obsolete chunk of code from make_file().
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f