Remove complex import rules

Per the discussion in [1], we are removing the import rules that
require introspection of the actual imported code due to the
complex and error-prone nature of those checks, and the fact that
some of them are simply impossible to implement sanely.

Checks that operate solely on the text of the import are left
alone because they should be less problematic.

[1]: http://lists.openstack.org/pipermail/openstack-dev/2014-December/052519.html

Change-Id: I43862a0d73706ee4b28951d5c8de6938c0cf5f27

HACKING.rst

@@ -41,12 +41,12 @@ General
 
 Imports
 -------
-- [H302] Do not import objects, only modules (*)
+- Do not import objects, only modules (*)
 - [H301] Do not import more than one module per line (*)
 - [H303] Do not use wildcard ``*`` import (*)
 - [H304] Do not make relative imports
-- Order your imports by the full module path
-- [H305 H306 H307] Organize your imports according to the `Import order
+- [H306] Order your imports by the full module path
+- Organize your imports according to the `Import order
   template`_ and `Real-world Import Order Examples`_ below.
 
 (*) exceptions are: