Reboot - delete useless parameter async, not supported (#80017)

Co-authored-by: baptch <b.jean.ch@gmail.com>
Co-authored-by: Sviatoslav Sydorenko <wk.cvs.github@sydorenko.org.ua>

changelogs/fragments/fix-reboot-plugin.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - Stopped misleadingly advertising ``async`` mode support in the ``reboot`` module (https://github.com/ansible/ansible/issues/71517).

lib/ansible/plugins/action/reboot.py

@@ -408,7 +408,6 @@ class ActionModule(ActionBase):
 
     def run(self, tmp=None, task_vars=None):
         self._supports_check_mode = True
-        self._supports_async = True
 
         # If running with local connection, fail so we don't reboot ourselves
         if self._connection.transport == 'local':