ModelLoadManager cleanup: Flip notified_about_ready_for_configure_

This CL changes ModelLoadManager::notified_about_ready_for_configure_
to delegate_waiting_for_ready_for_configure_, and accordingly inverts
its values.
The new name better reflects the actual semantics (e.g. previously, it
had to be set to "true" in cases where no configuration was ever
started).

No behavior changes.

Bug: 40901755
Change-Id: I3d694e54b1fbd80350e301f48fe6cc91385a3988
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5446922
Auto-Submit: Marc Treib <treib@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1287308}