Those are defined in Resource

src/atom/browser.coffee

@@ -6,8 +6,6 @@ module.exports =
 class Browser extends Resource
   window.resourceTypes.push this
 
-  url: null
-
   open: (url) ->
     return false if not /^https?:/.test url
 

src/atom/editor.coffee

@@ -15,10 +15,6 @@ class Editor extends Resource
 
   dirty: false
 
-  url: null
-
-  pane: null
-
   modeMap:
     js: 'javascript'
     c: 'c_cpp'