[io grant] Remove multi-dir &mkdir
[io grant] Remove multi-dir &mkdir

- Since mode arg is involved, we have a bit of a gnarly interface,
    since we have a case where $mode, $path and $path, $mode both work.
- The multi-dir multi is entirely untested
- There's exactly one case in the ecosystem that's using that multi by
    accident, because the user used the $mode, $path order of args
- By abandoning the multi, we can also take any Cools as path and mode

labster/rakudo,tony-o/rakudo,labster/rakudo,labster/rakudo,jonathanstowe/rakudo,awwaiid/rakudo,rakudo/rakudo,sjn/rakudo,softmoth/rakudo,usev6/rakudo,Gnouc/rakudo,tony-o/rakudo,softmoth/rakudo,rakudo/rakudo,salortiz/rakudo,lucasbuchala/rakudo,MasterDuke17/rakudo,sjn/rakudo,salortiz/rakudo,salortiz/rakudo,salortiz/rakudo,tony-o/rakudo,rakudo/rakudo,labster/rakudo,MasterDuke17/rakudo,tony-o/rakudo,softmoth/rakudo,MasterDuke17/rakudo,labster/rakudo,softmoth/rakudo,Gnouc/rakudo,nbrown/rakudo,lucasbuchala/rakudo,tbrowder/rakudo,labster/rakudo,nbrown/rakudo,nbrown/rakudo,MasterDuke17/rakudo,usev6/rakudo,raydiak/rakudo,salortiz/rakudo,nbrown/rakudo,awwaiid/rakudo,rakudo/rakudo,jonathanstowe/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,usev6/rakudo,lucasbuchala/rakudo,sjn/rakudo,raydiak/rakudo,nbrown/rakudo,sjn/rakudo,awwaiid/rakudo,raydiak/rakudo,lucasbuchala/rakudo,rakudo/rakudo,tony-o/rakudo,tbrowder/rakudo,awwaiid/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,raydiak/rakudo,Gnouc/rakudo,tbrowder/rakudo,usev6/rakudo,MasterDuke17/rakudo,sjn/rakudo,nbrown/rakudo,usev6/rakudo,jonathanstowe/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,tony-o/rakudo,tbrowder/rakudo,lucasbuchala/rakudo,rakudo/rakudo,Gnouc/rakudo,softmoth/rakudo,Gnouc/rakudo,awwaiid/rakudo,salortiz/rakudo