Replace AppUpdate::GetShowInManagement with AppUpdate::ShowInManagement.

DD:go/remove_mojom_in_app_service

AppService mojo is being removed. So modify AppUpdate::ShowInManagement
to get value from the non mojom App struct when it is available, and
remove AppUpdate::GetShowInManagement.

Modify tests to use and verify AppUpdate::ShowInManagement.

BUG=1253250

Change-Id: I2116ae307a7c5380113b4fe96255de49ee47ba59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3493378
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#975819}