[crd host][wayland] Fix infinite loop bug

The bug was introduced in crrev.com/c/6893890 where the erase() call was
removed when the monitor is not found and the iterator did not get
advanced, such that it loops infinitely if a preferred monitor config's
monitor is not/no longer found in the gnome display config, e.g. when
removing a monitor.

This CL fixes this by switching to the good old for-each loop.

Bug: 432217140
Change-Id: I73d2e68d4501637549d81bee0dfc18c1713fabd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6909985
Auto-Submit: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Commit-Queue: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1510364}