chore(templates): update Python version requirement and clean up versioned __init__.py.j2

Author: chalmerlowe

packages/gapic-generator/gapic/ads-templates/%namespace/%name/%version/__init__.py.j2

@@ -11,8 +11,8 @@ from {{package_path}} import gapic_version as package_version
 __version__ = package_version.__version__
 
 
-if sys.version_info < (3, 7):
-    raise ImportError('This module requires Python 3.7 or later.')
+if sys.version_info < (3, 8):
+    raise ImportError('This module requires Python 3.8 or later.')
 
 
 _lazy_type_to_package_map = {
@@ -37,14 +37,14 @@ _lazy_type_to_package_map = {
 
 
 # Background on how this behaves: https://www.python.org/dev/peps/pep-0562/
-def __getattr__(name):  # Requires Python >= 3.7
+def __getattr__(name):
     if name == '__all__':
         all_names = globals()['__all__'] = sorted(_lazy_type_to_package_map)
         return all_names
     elif name in _lazy_type_to_package_map:
         module = importlib.import_module(f'{_lazy_type_to_package_map[name]}')
         klass = getattr(module, name)
-        {# new_klass = type(name, (klass,), {'__doc__': klass.__doc__}) #}
+
         globals()[name] = klass
         return klass
     else: