Move accessibility extension translations to grd file.

ui/accessibility/extensions/alt/manifest.json

 {
   "name": "Replace images with alt text",
   "version": "0.1",
-  "description": "Replace images with their alt text",
+  "description": "__MSG_appDesc__",
   "background": {
     "scripts": [ "background.js" ]
   },
   "commands": {
     "example_keyboard_command": {
       "suggested_key": {
         "default": "Ctrl+Shift+I",
         "mac": "Ctrl+Shift+I"
       },
       "description": "Replace all images with their alt text."
     }
   },
   "browser_action": {
     "default_title": "Replace all images with their alt text.",
     "default_icon": {
       "19": "images/icon-19.png",
       "38": "images/icon-38.png"
     }
   },
-  "options_page": "options.html",
   "permissions": [
     "activeTab"
   ],
   "manifest_version": 2,
   "web_accessible_resources": [
     "images/speech-16.png",
     "images/speech-missing-alt-16.png",
     "images/statusbarButtonGlyphs.png"
   ]
 }