Remove non-MD code from VirtualKeyboardTray

ash/common/system/tray/tray_constants.h

Index: ash/common/system/tray/tray_constants.h
diff --git a/ash/common/system/tray/tray_constants.h b/ash/common/system/tray/tray_constants.h
index 1da6f92bfc20dc8b7ee73ce422533bf52e0841fd..e457f1dfd1ab1b17558e13fc4dac8b7a6c7f3213 100644
--- a/ash/common/system/tray/tray_constants.h
+++ b/ash/common/system/tray/tray_constants.h
@@ -171,12 +171,6 @@ enum TrayConstant {
   // The minimum default width for the right container of the system menu rows.
   TRAY_POPUP_ITEM_MIN_END_WIDTH,
 
-  // The width and height of the virtual keyboard button in the status tray
-  // area. For non-MD, adjustments are made to the button dimensions based on
-  // the shelf orientation, so this constant does not specify the true
-  // user-visible button bounds.
-  VIRTUAL_KEYBOARD_BUTTON_SIZE,
-
   // The icon size of opt-in IME menu tray.
   TRAY_IME_MENU_ICON,