Remove the callback parameter of removeTab()

callback parameter is never passed to removeTab(), so adding it to
the selectionChangeHandlers list causes 'Can not call method call() of undefined'
error after closing the tab.

background_scripts/main.coffee

@@ -234,12 +234,9 @@ BackgroundCommands =
   previousTab: (callback) -> selectTab(callback, "previous")
   firstTab: (callback) -> selectTab(callback, "first")
   lastTab: (callback) -> selectTab(callback, "last")
-  removeTab: (callback) ->
+  removeTab: ->
     chrome.tabs.getSelected(null, (tab) ->
-      chrome.tabs.remove(tab.id)
-      # We can't just call the callback here because we need to wait
-      # for the selection to change to consider this action done.
-      selectionChangedHandlers.push(callback))
+      chrome.tabs.remove(tab.id))
   restoreTab: (callback) ->
     # TODO(ilya): Should this be getLastFocused instead?
     chrome.windows.getCurrent((window) ->