Fix for new python.el

`python-python-command` and `python-python-command-args` are no longer used.

I got following error when I evaluate `M-x (django-python-command)`

```
Debugger entered--Lisp error: (void-variable python-python-command)
  (cons python-python-command python-python-command-args)
  (mapconcat (quote identity) (cons python-python-command python-python-command-args) " ")
  django-python-command()
  eval((django-python-command) nil)
  eval-expression((django-python-command) nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)
```