Remove the disableSelf() api

No longer needed, the logic will be handled in AttentionDetector which
implements the feature. Settings app makes sure to grey out the setting
if does not have sufficient permissions.

Bug: 130350903, 130246574
Test: manually confirmed, atest AttentionDetectorTests, make RunSettingsRoboTests
Change-Id: I324223af01b5198e3af0b84d47120f307f3aa71a