Revert "Add the option Require 'Confirm registrations' (Bug 1280882)"

This reverts commit 9b9e7e7ec3f78c551ef3b291d29e8586e7ec32b2.

New feature, shouldn't have been backported to a stable branch.

Change-Id: I7192922375dad1d7d425277f31ad4e9959c1c437