Remove theme customization settings in Message

Summary

Remove the theme customization in Message

This improvement concerns

• UI
• Behavior
• Privacy

Description

What is the current behavior?

It is possible to customize the color in Message, under Settings > Appearance > Theme

What is the improved behavior?

No possibility to modify the theme color from Message. The color used is the one from System accent color (see #1718 (closed))

What does it bring?

Consistency

Examples

Validation