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
this should look like this:

```
def main():
    L = [1]
    for i in range(1, N):
        L.append(cos(i*x))
        L.append(sin(i*x))
    # next 2 lines equivalent to l2_gram_schmidt(L, (x, -pi, pi)), but faster:
    L[0] = L[0]/sqrt(2)
    L = [f/sqrt(pi) for f in L]

    f = ...
```