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
```
# if the result is too complex the user might consider `simplify(result.expand(complex=True))`
```

Such a note might be better for the docstring.