Remove old (dead) app list code.

ui/app_list/search_box_model.cc

Index: ui/app_list/search_box_model.cc
diff --git a/ui/app_list/search_box_model.cc b/ui/app_list/search_box_model.cc
index e8494de58d6dc4c3b7ef6c05ccbbe4f9e6462032..aa29fccff7c0fdfb58af72b2b48f8c69854e91a6 100644
--- a/ui/app_list/search_box_model.cc
+++ b/ui/app_list/search_box_model.cc
@@ -33,11 +33,6 @@ SearchBoxModel::SearchBoxModel() {
 SearchBoxModel::~SearchBoxModel() {
 }
 
-void SearchBoxModel::SetIcon(const gfx::ImageSkia& icon) {
-  icon_ = icon;
-  FOR_EACH_OBSERVER(SearchBoxModelObserver, observers_, IconChanged());
-}
-
 void SearchBoxModel::SetSpeechRecognitionButton(
     std::unique_ptr<SearchBoxModel::SpeechButtonProperty> speech_button) {
   speech_button_ = std::move(speech_button);