Remove RootTargetPreparer from art_standalone_artd_tests.

This test is part of ART MTS. We cannot use root because MTS runs on
user builds. In fact, most of the test cases don't need root.

This CL skips a test case that requires root. The test case will be
fixed later. Tracked by b/289037540.

Bug: 288989992
Test: atest art_standalone_artd_tests
Change-Id: I111c5d42c1020c353cbf5eebb0e49f26ea5bc2cb
Merged-In: I111c5d42c1020c353cbf5eebb0e49f26ea5bc2cb