executor: Remove RETURN_VARS (#86527)

RETURN_VARS was introduced for #70331, and last used in #70853.

    # git grep RETURN_VARS | wc -l
    1

Remove it.

Signed-off-by: Ariel Otilibili <a.otilibili@instadeep.com>

changelogs/fragments/ansible-executor-remove-return-vars.yml

@@ -0,0 +1,3 @@
+---
+minor_changes:
+  - executor - remove unused RETURN_VARS

lib/ansible/executor/task_executor.py

@@ -49,7 +49,6 @@ if t.TYPE_CHECKING:
 display = Display()
 
 
-RETURN_VARS = [x for x in C.MAGIC_VARIABLE_MAPPING.items() if 'become' not in x and '_pass' not in x]
 _INJECT_FACTS, _INJECT_FACTS_ORIGIN = C.config.get_config_value_and_origin('INJECT_FACTS_AS_VARS')
 
 __all__ = ['TaskExecutor']