Fix the wrong test fixture setup regarding downgrade.

The storage threshold is now controlled by a constant rather than a
sysprop. This change removes the setup for the sysprop that no longer
exsits and adds a test case to catch such wrong setup.

Also fixes a wrong comment.

Bug: 255565888
Test: atest ArtServiceTests
Ignore-AOSP-First: ART Services.
Change-Id: Ib902e643a528a47ec5d0c3a3b1751d3d9d6f6d90
2 files changed