chore(test): remove redundant TestsSetUp.cs

The SetUpFixture doesn't prevent "Bake Ambient Probe" errors since they
come from Unity's BuildPipeline, not scene creation. JEngineTestBase
already handles error suppression per-test via LogAssert.ignoreFailingMessages.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: JasonXuDeveloper - 傑 <jason@xgamedev.net>

Author: JasonXuDeveloper