Remove support for Sites API

[taers232c]

The sites API no longer functions; support for classic sites should be removed.

$ gam print sites              
Getting all Sites for Domain: auroraschool.org
Traceback (most recent call last):
  File "__init__.py", line 77536, in ProcessGAMCommand
  File "__init__.py", line 42825, in doPrintShowDomainSites
  File "__init__.py", line 42808, in printShowSites
  File "__init__.py", line 42673, in _getSites
  File "__init__.py", line 5115, in callGDataPages
  File "__init__.py", line 5050, in callGData
  File "gdata/apps/sites/service.py", line 76, in get_site_feed
  File "gdata/service.py", line 1093, in Get
  File "gdata/service.py", line 1065, in Get
  File "atom/__init__.py", line 76, in optional_warn_function
  File "atom/service.py", line 148, in request
AttributeError: 'int' object has no attribute 'items'

[jay0lee]

Good riddance?

This brings us one step closer to #1656

[taers232c]

Removed in 7.04.00