Use a mock response parser in OnDeviceModelFeatureAdapter tests

This decouples the unit tests from the concrete ReportParser types so
that the OnDeviceModelFeatureAdapter functionality can be exercised
in isolation. Removes the DefaultSimple and JSON tests since this
functionality is already exercised in their respective ReportParser
tests. The NoOutputConfig test was actually exercising logic in
SimpleResponseParser, so this is replaced with an empty proto test on
that class.

Bug: 383761415
Change-Id: I183ba1f78844c2c590193e4e9b3c05ec6b0cd6f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6553091
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1461449}