Remove dead code from _eval_subs()
completed by: David Ju
mentors: Matthew Rocklin, Vladimir Perić, Stefan Krastanov, Aaron Meurer
Please see http://code.google.com/p/sympy/issues/detail?id=654 for full information on this task.
Please read https://github.com/sympy/sympy/wiki/gci-2011-landing before completing any tasks for SymPy.