[iOS] Remove contentNeedsAuthenticationChanged from delegate

This delegate function was only used to update toolbar's button when
incognito grid needs authentication. This update is now manage from
the incognito grid mediator so this CL remove the function as it is not
necessary anymore.

Bug: 1457146
Change-Id: I2b9195feeda60f22b4d45e5febceac0b782ce7f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4974449
Reviewed-by: Louis Romero <lpromero@google.com>
Commit-Queue: Louis Romero <lpromero@google.com>
Auto-Submit: Aliona Dangla <alionadangla@chromium.org>
Commit-Queue: Aliona Dangla <alionadangla@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1218838}