chromeos: Remove AshTestBase::SupportsMultipleDisplays

ash/test/ash_test_base.h

Index: ash/test/ash_test_base.h
diff --git a/ash/test/ash_test_base.h b/ash/test/ash_test_base.h
index 9d7bca1c0ce1dbd63f6d935fa7681d2065a5ed09..8b81b2be0e72a5dbb4a6a4bac915b93cf813aad2 100644
--- a/ash/test/ash_test_base.h
+++ b/ash/test/ash_test_base.h
@@ -138,9 +138,6 @@ class AshTestBase : public testing::Test {
   // Returns the rotation currently active for the internal display.
   static display::Display::Rotation GetCurrentInternalDisplayRotation();
 
-  // Proxy to AshTestHelper::SupportsMultipleDisplays().
-  static bool SupportsMultipleDisplays();
-
   void set_start_session(bool start_session) { start_session_ = start_session; }
 
   // Sets material mode for the test. This will override material mode set via