In wheel-to-egg conversion, use simple pkg_resources-style namespace...

In wheel-to-egg conversion, use simple pkg_resources-style namespace declaration for packages that declare namespace_packages. Fixes #2070.

setuptools/wheel.py

@@ -27,12 +27,8 @@ WHEEL_NAME = re.compile(
     )\.whl$""",
     re.VERBOSE).match
 
-NAMESPACE_PACKAGE_INIT = '''\
-try:
-    __import__('pkg_resources').declare_namespace(__name__)
-except ImportError:
-    __path__ = __import__('pkgutil').extend_path(__path__, __name__)
-'''
+NAMESPACE_PACKAGE_INIT = \
+    "__import__('pkg_resources').declare_namespace(__name__)\n"
 
 
 def unpack(src_dir, dst_dir):