Remove KeyMap binding for Brightness dialog

[stefanhahmann]

User Story

The brightness settings dialog does not exist anymore as a separate dialog in Mastodon. Instead, this functionality can be accessed via the Big Data Viewer Side Panel, cf. #285 for more information.

It is still possible however to define a KeyMap binding for this not anymore existing function. This is confusing.

As a user, I would like that this KeyMap binding is removed, since the function cannot be accessed via a KeyBinding anymore.

Acceptance criteria:

1. Brightness settings command does not appear in the KeyMap bindings dialog anymore.