While testing MDL-69088 we found that there are a bunch of functions that do more or less the same thing:

lib/filelib.php fulldelete()

lib/moodlelib.php remove_dir()

backup/cc/cc_lib/gral_lib/pathutils.php:403:function rmdirr($dirname)

There are all also very slow at scale because they process all the files recursively directly in php.

I'm proposing:

a) pick one and refactor the others to just call it, and deprecate them

b) In a similar way to pathtodu have an option to use a cli variant which unlinks the directory outside of php land which should be more or less instant.