Get rid of some unnecessary commented out code (issue #6849)

There is a lot of false positives (see [attached logs](http://code.google.com/p/sympy/issues/detail?id=3750#c1)), so I don't think that we should automate such cleanup.

fixes #6849
On Thu, Oct 16, 2014 at 02:26:06PM -0700, Christopher Smith wrote:
>    In sympy/printing/pretty/pretty.py:
> 
>  > @@ -367,11 +366,6 @@ def _print_Integral(self, integral):
>  >                  pform = prettyForm(*pform.above(prettyB))
>  >                  pform = prettyForm(*pform.below(prettyA))
>  >
>  > -                #if ascii_mode:  # XXX hack
> 
>    It represents a TODO

Apparently, this is bad place for TODO.  Esp. to keep todo
here for ~7 years.  (This code was introduced by 8d8189d).
We have github issues to keep issues, right?