[Extensions c2s] Refactor HasAction in ExtensionsMenuTestUtil

ExtensionsMenuTestUtil::HasAction is used by callers to verify whether
an extension has an action in the toolbar. The action doesn't need to
be retrieved from the menu. Instead, we can verify whether the
extensions container has an action for the extension.

Bug: 40889653, 373672171
Change-Id: I8028bc040811a9d1532add7fba1423ce393fe602
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5950556
Commit-Queue: Emilia Paz <emiliapaz@chromium.org>
Reviewed-by: Justin Lulejian <jlulejian@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1372339}