Chart: Remove unused frame/background stuff from legend

Authored by danders on Apr 13 2018, 9:46 AM.

Description

Chart: Remove unused frame/background stuff from legend

Summary:
Remove setter/getters and ui.

These things are controlled from the Shape Tool,
so the KChart things shall not be used.

Reviewers: #calligra:_3.0, leinir, mecir, boemann

Reviewed By: leinir

Tags: #calligra:_3.0

Differential Revision: https://phabricator.kde.org/D12169