feat: drop namespacing hooks

pkg_resources is deprecated.
Since Python 3.3 there is native namespacing.
But this requires that no __init__.py exists, therefore not usable here.

in case we need it, e.g. to support httoop-http2 we can still use
`__path___ = __import__('pkgutil').extend_path(__path__, __name__)`.

Author: spaceone

httoop/__init__.py

@@ -51,8 +51,3 @@
     '__version__', 'ServerProtocol', 'UserAgentHeader', 'ServerHeader',
     'cache', 'ComposedRequest', 'ComposedResponse',
 ]
-
-try:
-    __import__('pkg_resources').declare_namespace(__name__)
-except ImportError:  # pragma: no cover
-    __path___ = __import__('pkgutil').extend_path(__path__, __name__)