removes duplicate entry from requirements.txt for 'bleach'

I was installing dependencies then it raised me following error, for a duplicate entry in the file.
> Double requirement given: bleach (from -r requirements.txt (line 22)) (already in bleach (from -r requirements.txt (line 16)), name='bleach')

I am using `pip` version `1.3.1`

So this commit removes that duplicate entry.