[orca-list] Proposal: Remove the "alternative keybinding" support from Orca

[Joanmarie Diggs <jdiggs igalia com>]

Hey all.

Given that:
* All alternative keybindings which Orca comes with by default no
  longer exist, having been removed when we re-enabled NumPad keys.
* You can bind, rebind, and unbind keybindings as you need to.
* You can use profiles if you sometimes need one keybinding for a
  command and other times another keybinding for that same command.
* You can manually add alternative bindings via orca-customizations.py.

I propose the following:

1. We remove the alternative keybinding column from Orca's GUI (along
   with the code required to support populating and managing them in
   that tree).
2. We add official documentation to Orca which explains how to add an
   alternative binding via orca-customizations.py for those rare 
   occasions this functionality simply must be had.

Discussion? +1/-1?

Thanks and take care.
--joanie