chromeos: Remove AshTestBase::SupportsMultipleDisplays

ash/wm/immersive_fullscreen_controller_unittest.cc

Index: ash/wm/immersive_fullscreen_controller_unittest.cc
diff --git a/ash/wm/immersive_fullscreen_controller_unittest.cc b/ash/wm/immersive_fullscreen_controller_unittest.cc
index 7adb754d51375483dcc00a4544b5462db7880357..a9665e5fddb555b4d133635f86933275d85bf773 100644
--- a/ash/wm/immersive_fullscreen_controller_unittest.cc
+++ b/ash/wm/immersive_fullscreen_controller_unittest.cc
@@ -496,9 +496,6 @@ TEST_F(ImmersiveFullscreenControllerTest, Inactive) {
 // has a vertical display layout (primary display above/below secondary display)
 // and the immersive fullscreen window is on the bottom display.
 TEST_F(ImmersiveFullscreenControllerTest, MouseEventsVerticalDisplayLayout) {
-  if (!SupportsMultipleDisplays())
-    return;
-
   // Set up initial state.
   UpdateDisplay("800x600,800x600");
   ash::Shell::GetInstance()->display_manager()->SetLayoutForCurrentDisplays(