Remove the deprecated Alt+Shift shortcut completely

ash/ash_chromeos_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- ChromeOS-specific strings (included from ash_strings.grd).
      Everything in this file is wrapped in <if expr="chromeos">. -->
 <grit-part>
 
   <!-- Device types -->
   <message name="IDS_ASH_CHROMEBASE" desc="The device name for a Chromebase (versus say Chromebox)">
     Chromebase
   </message>
   <message name="IDS_ASH_CHROMEBIT" desc="The device name for a Chromebit (versus say Chromebox)">
@@ skipping 594 matching lines @@
   </message>
   <message name="IDS_SHORTCUT_LOCK_SCREEN_NEW" desc="the new shortcut to lock the screen.">
     Search+L
   </message>
   <message name="IDS_SHORTCUT_TASK_MANAGER_OLD" desc="the old deprecated shortcut to open the task manager.">
     Shift+Esc
   </message>
   <message name="IDS_SHORTCUT_TASK_MANAGER_NEW" desc="the new shortcut to open the task manager.">
     Search+Esc
   </message>
-  <message name="IDS_SHORTCUT_NEXT_IME_OLD" desc="the old deprecated shortcut to switch to the next input method.">
-    Shift+Alt
-  </message>
-  <message name="IDS_SHORTCUT_NEXT_IME_NEW" desc="the new shortcut to switch to the next input method.">
-    Ctrl+Shift+Space
-  </message>
   <message name="IDS_DEPRECATED_LOCK_SCREEN_MSG"
            desc="Notification message to tell users about the deprecation of Ctrl+Shift+L shortcut to lock the screen.">
     The shortcut to lock the screen has changed. Please use <ph name="NEW_SHORTCUT">$1<ex>Search+L</ex></ph> instead of <ph name="OLD_SHORTCUT">$2<ex>Ctrl+Shift+L</ex></ph>.
   </message>
   <message name="IDS_DEPRECATED_SHOW_TASK_MANAGER_MSG"
            desc="Notification message to tell users about the deprecation of Shift+ESC shortcut to show the task manager.">
     The shortcut to open the task manager has changed. Please use <ph name="NEW_SHORTCUT">$1<ex>Search+Esc</ex></ph> instead of <ph name="OLD_SHORTCUT">$2<ex>Shift+Esc</ex></ph>.
   </message>
-  <message name="IDS_DEPRECATED_NEXT_IME_MSG"
-           desc="Notification message to tell users about the deprecation of Shift+Alt shortcut to switch to the next input method.">
-    The shortcut to switch to the next input method has changed. Please use <ph name="NEW_SHORTCUT">$1<ex>Ctrl+Shift+Space</ex></ph> instead of <ph name="OLD_SHORTCUT">$2<ex>Shift+Alt</ex></ph>.
-  </message>
 
   <!-- Notification that an accelerator was pressed, so the user knows how to toggle it back -->
   <message name="IDS_HIGH_CONTRAST_ACCEL_MSG"
            desc="Notification message to tell users that they just pressed the Search+Shift+H shortcut to toggle High Contrast Mode, and that pressing it again will toggle it off.">
     High Contrast Mode enabled. Press Search+Shift+H again to toggle it off.
   </message>
 </grit-part>