R1:378d4380d381

Fix visibility of the `LiskDAO::willWriteData` method

Summary: Ref T6822.

Test Plan: `grep`. This method is only called from `LiskDAO::update()`.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T6822

Differential Revision: https://secure.phabricator.com/D11409