vim: from now, folding is not activated by default in python files

Due to some erratic behavior folding some functions in python, I decided to no
fold them automatically by default when a python file is opened. And you know,
because is a little irritant having all the folders unfolded, save the file and
wow, all of them are folded again!. So I get tired of this.

Still is possible to fold/unfold them by hand at your convenience.