[ESS] disabling C-c h bound to ess-handy-commands

[Stephen Eglen]

> Here is a constructive proposal:
>
> C-c C-e ess-extra-map (includes roxygen, which already hands on it)
> C-c C-d ess-doc-map (ess-dump-object-into-edit-buffer is moved onto C-c C-e C-e)
> C-c C-d ess-dev-map (ess-execute-in-tb is moved on C-c C-e C-t)
> C-c C-a ess-handy-commands
>
seems good to me.

> Remove C-c C-y (C-c C-z does the job and is faster)
> Remove C-c C-k (C-c C-s should be enough and is faster)
yes.

> ;; Not very sure about this one:
> Remove C-c C-f (C-c C-c and C-M-x do that anyways)
yes. my vote would be to remove this current binding.