Issue 6620 - Update extension description

_locales/en_GB/messages.json

 {
   "add": {
     "message": "Add"
   },
   "add_domain_button": {
     "message": "Add domain"
   },
   "add_filter_button": {
     "message": "Add filter"
   },
@@ skipping 11 matching lines @@
   },
   "cancel": {
     "message": "Cancel"
   },
   "clickhide_instructions": {
     "message": "After closing this popup, click (or right-click) an element on the page."
   },
   "continue": {
     "message": "Continue"
   },
-  "description": {
-    "message": "Used on over 100 million devices, Adblock Plus is the world's most popular ad blocker."
-  },
   "disabled_for_site": {
     "message": "<strong>Disabled</strong> on this site"
   },
   "disabled_for_these_domains": {
     "message": "Adblock Plus is disabled for the domains listed below. You can add a domain either via the Adblock Plus icon in the address bar or by typing the domain (not a URL) in the box and clicking the \"Add domain\" button."
   },
   "easy_create_filter": {
     "message": "Block element"
   },
   "edit_filters_raw": {
@@ skipping 205 matching lines @@
   "unexpected_filter_list_header": {
     "message": "Filter list headers aren't allowed here"
   },
   "update_now": {
     "message": "Update now"
   },
   "whitelisted_domains": {
     "message": "Whitelisted domains"
   }
 }