Settings: update documentation for REQUIRE_PASSWORD_TO_DECRYPT

This setting no longer does anything, so update its documentation.  I'd
rather just remove it entirely, or at least deprecate it, but it's
unclear that either is allowed by the API guidelines.

Bug: 208476087
Change-Id: I031e9f4316d76634350deea211767e8390e5c4f3
1 file changed