Development settings: Remove icon from root dialog

* Other dialogs in development settings don't have an icon anymore

Change-Id: If7784cf8d758ccce6d8dd3c2bae49ec8c6303336
Revert "Introduce SystemSettingsCheckBoxPreference"

This reverts commit 3223e2d7b2eca1629b3466de0de4a8c31e5f3415.
Add back a helper pref that holds a system setting.

Change-Id: I7d8978829bde1f1dd15bf59f464557f64aa07beb
Fix build

Change-Id: I1d64a935f0c96991eeacd5417f42d1020910cfb0