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

[Stephen Eglen]

>
> That means finding handy shortcuts for ess-handy-commands, ess-dev-map
> and ess-set-style:
>
>
> C-c .           ess-set-style
> C-c `           ess-parse-errors

(These first two seem to be okay to bind -- see the info; it just
prohibits C-c LETTER).

> C-c d           ess-dev-map
> C-c h           ess-handy-commands
>
I think there is nothing wrong with us recommending to users that they
use those bindings - but I think we should stay clear of installing them
by default.

Stephen