Simplify deprecation mechanism

Co-Authored-By: Sloane Hertel <19572925+s-hertel@users.noreply.github.com>
Co-Authored-By: Matt Martz <matt@sivel.net>

lib/ansible/utils/plugin_docs.py

@@ -14,7 +14,7 @@ from ansible.module_utils.common.text.converters import to_native
 from ansible.parsing.plugin_docs import read_docstring
 from ansible.parsing.yaml.loader import AnsibleLoader
 from ansible.utils.display import Display
-import functools
+from ansible.utils.sentinel import Sentinel
 
 display = Display()
 
@@ -205,20 +205,14 @@ def add_fragments(doc, filename, fragment_loader, is_module=False):
         raise AnsibleError('unknown doc_fragment(s) in file {0}: {1}'.format(filename, to_native(', '.join(unknown_fragments))))
 
 
-def _handle_deprecated_kwarg(func):
-    @functools.wraps(func)
-    def wrapper(*args, **kwargs):
-        if len(args) >= 6 or 'is_module' in kwargs:
-            display.deprecated("is_module is deprecated, pass plugin_type='module' instead", version='2.19')
-        return func(*args, **kwargs)
-    return wrapper
-
-
-@_handle_deprecated_kwarg
-def get_docstring(filename, fragment_loader, verbose=False, ignore_errors=False, collection_name=None, is_module=None, plugin_type=None):
+def get_docstring(filename, fragment_loader, verbose=False, ignore_errors=False, collection_name=None, is_module=Sentinel, plugin_type=None):
     """
     DOCUMENTATION can be extended using documentation fragments loaded by the PluginLoader from the doc_fragments plugins.
     """
+    if is_module is Sentinel:
+        is_module = None
+    else:
+        display.deprecated("is_module is deprecated, pass plugin_type='module' instead", version='2.19')
 
     if is_module is None:
         if plugin_type is None: