chromeos: Remove AshTestBase::SupportsMultipleDisplays

ui/display/manager/display_manager.cc

Index: ui/display/manager/display_manager.cc
diff --git a/ui/display/manager/display_manager.cc b/ui/display/manager/display_manager.cc
index 24c74f0c083ffe528802f2d0541f5fd9d63f13e6..dc9160e6be3b3643ec3faec4a9d7884764196972 100644
--- a/ui/display/manager/display_manager.cc
+++ b/ui/display/manager/display_manager.cc
@@ -636,7 +636,7 @@ void DisplayManager::UpdateDisplaysWith(
 #if defined(OS_WIN)
   DCHECK_EQ(1u, updated_display_info_list.size())
       << ": Multiple display test does not work on Windows bots. Please "
-         "skip (don't disable) the test using SupportsMultipleDisplays()";
+         "skip (don't disable) the test.";
 #endif
 
   DisplayInfoList new_display_info_list = updated_display_info_list;