cros-md: Remove the non-MD immersive mode code paths

ash/common/material_design/material_design_controller.cc

Index: ash/common/material_design/material_design_controller.cc
diff --git a/ash/common/material_design/material_design_controller.cc b/ash/common/material_design/material_design_controller.cc
index 6cf3b9865488a27eded166ffdee4b4cae2002e2d..dd8a25a73a4641f9a8cc22d17320b7849b8cea65 100644
--- a/ash/common/material_design/material_design_controller.cc
+++ b/ash/common/material_design/material_design_controller.cc
@@ -14,11 +14,6 @@ bool MaterialDesignController::IsShelfMaterial() {
 }
 
 // static
-bool MaterialDesignController::IsImmersiveModeMaterial() {
-  return true;
-}
-
-// static
 bool MaterialDesignController::IsSystemTrayMenuMaterial() {
   return true;
 }