Removed focus handling workaround for editor tab changes (#89, #327).

The issue the workaround was for was already fixed in wxwidgets:
http://trac.wxwidgets.org/ticket/14142

src/editor/gui.lua

@@ -173,13 +173,6 @@ local function createNotebook(frame)
         and debug:traceback():find("'AddPage'"))
 
       if doc and event:GetOldSelection() ~= -1 and not double then
-        -- switching between editor tabs doesn't trigger KILL_FOCUS events
-        -- on OSX (http://trac.wxwidgets.org/ticket/14142); trigger manually
-        if ide.osname == 'Macintosh' then
-          local win = notebook:GetPage(event:GetOldSelection())
-          local ev = wx.wxFocusEvent(wx.wxEVT_KILL_FOCUS)
-          win:GetEventHandler():ProcessEvent(ev)
-        end
         SetEditorSelection(notebook:GetSelection())
       end
     end)