Remove support for page_action.icons, and the legacy code surrounding it.

chrome/common/extensions/api/page_action.json

 // 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.
 
 [
   {
     "namespace": "pageAction",
     "dependencies": [ "tabs" ],
     "types": [
       {
@@ skipping 97 matching lines @@
                       "38": {"type": "string", "optional": true}
                     }
                   }
                 ],
                 "optional": true,
                 "description": "Either a relative image path or a dictionary {size -> relative image path} pointing to icon to be set. If the icon is specified as a dictionary, the actual image to be used is chosen depending on screen's pixel density. If the number of image pixels that fit into one screen space unit equals <code>scale</code>, then image with size <code>scale</code> * 19 will be selected. Initially only scales 1 and 2 will be supported. At least one image must be specified. Note that 'details.path = foo' is equivalent to 'details.imageData = {'19': foo}'"
               },
               "iconIndex": {
                 "type": "integer",
                 "minimum": 0,
-                "description": "<b>Deprecated.</b> The zero-based index into the <b>icons</b> vector specified in the manifest.",
+                "description": "<b>Deprecated.</b> This argument is ignored.",
                 "optional": true
               }
             }
           },
           {
             "type": "function",
             "name": "callback",
             "optional": true,
             "parameters": []
           }
@@ skipping 53 matching lines @@
         "parameters": [
           {
             "name": "tab",
             "$ref": "tabs.Tab"
           }
         ]
       }
     ]
   }
 ]