Restrictions: Clarify "non-Admin" not "secondary"

These UserRestrictions say that they have no affect on secondary users
due to their inability to access the underlying Settings.
But in reality, Admin users (even if secondary users) can also access
them, so the statement was incorrect.

Other parts of these javadocs may also need updating (related to
policies set on primary users), but that's beyond the scope of this
change.

Test: Manually confirmed that non-Admins cannot access these in Settings
Bug: 359912575
Flag: EXEMPT just javadoc
Change-Id: Ifd9174e00aee87875a8bccaf34fb42d05b8639c6