remove ntp app install hint

chrome/browser/resources/ntp4/new_tab_theme.css

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file. */
 
 html {
   background-attachment: fixed;
   background-color: $2;  /* COLOR_NTP_BACKGROUND */
   background-image: url(chrome://theme/IDR_THEME_NTP_BACKGROUND?$1);
   background-position: $3;
   background-repeat: $5;
@@ skipping 89 matching lines @@
 }
 
 .thumbnail-wrapper {
   /* This shows through at the (rounded) thumbnail's corners. */
   background-color: $11;  /* COLOR_NTP_SECTION_BORDER */
 }
 
 .filler .thumbnail {
   border-color: $2;  /* COLOR_NTP_BACKGROUND */
 }
-
-/* App install hint ***********************************************************/
-
-.app-install-hint:hover .app-install-hint-interior > .interior-background,
-.app-install-hint:active .app-install-hint-interior > .interior-background {
-  background-color: rgba($23, 0.2);  /* COLOR_NTP_SECTION_BORDER */
-}
-
-.app-install-hint-interior > .vertical-bar,
-.app-install-hint-interior > .horizontal-bar {
-  background-color: $21;  /* COLOR_NTP_TEXT_LIGHT */
-}
-
-.app-install-hint-interior {
-  border-color: $21;  /* COLOR_NTP_TEXT_LIGHT */
-}