ThemePicker: disable color picker for custom theme

• /e/ version: q, r
• Device model(s):
• Device rooted: yes/no

Summary

As discussed in https://gitlab.e.foundation/e/backlog/-/issues/4510#note_144391, we want to hide disable choosing accent color from styles & wallpaper menu of settings app.

The problem

Steps to reproduce

1. Go to settings
2. Go to display
3. Go to styles and wallpapers.
4. Go to style
5. Create custom
6. Go through setup until you get to color

What is the current behavior?

Multiple color option becomes available for user.

What is the expected correct behavior?

Only default accent color should be available for user.

Technical informations

Relevant logs (adb logcat)

Relevant screenshots

Solutions

Workaround

Possible fixes