This reverts the `PasswordFormManagerObserver` related code on IOS to
the state prior to
https://chromium-review.googlesource.com/c/chromium/src/+/6703663.

The changes ended up causing crashes (crbug.com/441585012 ). So far we
were not able to reproduce the crashes, so we need to revert as the
crash is release-blocking for stable.

BYPASS_RECITATION_REASON=reverting code

(cherry picked from commit 12e010188ce106b609f26e74f32e5e7119a492dd)

Bug: 441585012
Change-Id: I0ae7c236ba3d33f4612ed4103f847f9efdcf862a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6898279
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Oleksandr Tara <otara@google.com>
Cr-Original-Commit-Position: refs/heads/main@{#1508417}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6899779
Reviewed-by: Krishna Govind <govind@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Krishna Govind <govind@chromium.org>
Cr-Commit-Position: refs/branch-heads/7383@{#4}
Cr-Branched-From: 79ec61cd0754248b5a3533692e225be19ac1c15b-refs/heads/main@{#1508316}