Co-authored-by: Marc Cornellà <hello@mcornella.com>

Replace the alias with a function. Call `dirs` if arguments are given to `d`.

https://github.com/robbyrussell/oh-my-zsh/issues/6761

The alias was removed in #3564. A couple of users were using
it, so I'm adding it back.

The -h options in l, ll, and la were lost in 25b1cd68. There's no reason
to remove them.

- Cleans out aliases.zsh.
- Removes unneeded cd function.

From http://zsh.sourceforge.net/Doc/Release/Options.html#Completion-4

> AUTO_NAME_DIRS
> Any parameter that is set to the absolute name of a directory immediately
> becomes a name for that directory, that will be used by the ‘%~’ and
> related prompt sequences, and will be available when completion is performed
> on a word starting with ‘~’.
> (Otherwise, the parameter must be used in the form ‘~param’ first.)

Explained in more detail in
https://github.com/wayneeseguin/rvm/issues/3091#issuecomment-60083194

Related issues:
https://github.com/robbyrussell/oh-my-zsh/issues/2857
https://github.com/robbyrussell/oh-my-zsh/issues/3238
https://github.com/wayneeseguin/rvm/issues/3091

oh-my-zsh.

Modify directory listing aliases to make more sense. Remove conflicting helper
function (mcd conflicts with mtools).