Remove Python 2 compatibility code

[Patrick Sanders]

We're no longer compatible with Python 2, so we can remove all of the compatibility workarounds.

For example:

aardvark/aardvark/manage.py

Lines 24 to 32 in 5926d03

 try:               # Python 2 
     raw_input 
 except NameError:  # Python 3 
     raw_input = input 
  
 try:               # Python 2 
     unicode 
 except NameError:  # Python 3 
     unicode = str 

This block can be removed and the code updated to use str and input.