Remove experimental permission.

remoting/webapp/app_remoting/manifest_common.json.jinja2

   {{ MANIFEST_KEY_FOR_UNOFFICIAL_BUILD }}
   "name": "{{APP_NAME}}",
   "description": "{{APP_DESCRIPTION}}",
   "version": "{{ FULL_APP_VERSION }}",
   "manifest_version": 2,
   "default_locale": "en",
   "app": {
     "background": {
       "scripts": ["ar_background.js", "platform.js"]
     }
   },
   "icons": {
     "128": "icon128.png",
     "48": "icon48.png",
     "16": "icon16.png"
   },
   "optional_permissions": [
     "<all_urls>"
   ],
   "permissions": [
     "{{ APP_REMOTING_API_BASE_URL }}/*",
     "{{ DIRECTORY_API_BASE_URL }}/*",
     "{{ OAUTH2_ACCOUNTS_HOST }}/*",
     "{{ OAUTH2_API_BASE_URL }}/*",
     "{{ TALK_GADGET_HOST }}/talkgadget/*",
     "app.window.shape",
     "clipboardRead",
     "clipboardWrite",
     "contextMenus",
-    "experimental",
     "fileSystem",
     "fullscreen",
     "https://relay.google.com/*",
     "identity",
     "pointerLock",
     "storage",
     {
       "socket": [
         "udp-send-to",
         "udp-bind",
@@ skipping 10 matching lines @@
   },
   "oauth2": {
     "client_id": "{{ REMOTING_IDENTITY_API_CLIENT_ID }}",
     "scopes": [
       "https://www.googleapis.com/auth/appremoting.runapplication https://www.googleapis.com/auth/googletalk https://www.googleapis.com/auth/userinfo#email https://www.googleapis.com/auth/userinfo.profile {{ OAUTH_GDRIVE_SCOPE }}"
     ]
   },
   "sandbox": {
     "pages": [ "wcs_sandbox.html" ]
   }