Get rid of external teardown trigger because #245 resolves the problem

tractor/trionics/_mngrs.py

@@ -17,7 +17,6 @@ async def _enter_and_wait(
     mngr: AsyncContextManager[T],
     unwrapped: dict[int, T],
     all_entered: trio.Event,
-    teardown_trigger: trio.Event,
 ) -> None:
     '''Open the async context manager deliver it's value
     to this task's spawner and sleep until cancelled.
@@ -29,18 +28,13 @@ async def _enter_and_wait(
         if all(unwrapped.values()):
             all_entered.set()
 
-        await teardown_trigger.wait()
+        await trio.sleep_forever()
 
 
 @acm
 async def async_enter_all(
     mngrs: Sequence[AsyncContextManager[T]],
-    teardown_trigger: trio.Event,
 ) -> AsyncGenerator[tuple[T, ...], None]:
-    """This async context manager expects a 'teardown_trigger' from the
-    outside world which will be used internally to gracefully teardown
-    individual context managers.
-    """
     unwrapped = {}.fromkeys(id(mngr) for mngr in mngrs)
 
     all_entered = trio.Event()
@@ -52,10 +46,11 @@ async def async_enter_all(
                 mngr,
                 unwrapped,
                 all_entered,
-                teardown_trigger,
             )
 
         # deliver control once all managers have started up
         await all_entered.wait()
 
         yield tuple(unwrapped.values())
+
+        n.cancel_scope.cancel()