Squish: Cleanup tst_simple_debug

Change-Id: Ie74b0dd42d14e594e436408e39db20554904b84e
Reviewed-by: Robert Loehning <robert.loehning@digia.com>

tests/system/suite_debugger/tst_simple_debug/test.py

 source("../../shared/qtcreator.py")
 
-workingDir = None
-
 def main():
-    global workingDir
     startApplication("qtcreator" + SettingsPath)
     if not startedWithoutPluginError():
         return