Drop #16488 patch
Our #16488 (moved) patch was intended to hide the Sign in to Sync button in the hamburger menu. Unfortuately, reviewers at Mozilla weren't sure it was a good idea, and then it stopped working correctly when I rebased to FF45ESR.
We introduced torbutton patch #18743 (moved) instead. So I believe we can revert (or remove) our #16488 (moved) patch from tor-browser.git.