Remove Service.tasks property

This is revealing too much internal information about how a service can
be implemented, it makes more sense to expose it only to classes
implementing a service, but not to service users.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/core/asyncio/_service.py

@@ -59,19 +59,6 @@ def start(self) -> None:
     def unique_id(self) -> str:
         """The unique ID of this service."""
 
-    @property
-    @abc.abstractmethod
-    def tasks(self) -> collections.abc.Set[asyncio.Task[Any]]:
-        """The set of running tasks spawned by this service.
-
-        Users typically should not modify the tasks in the returned set and only use
-        them for informational purposes.
-
-        Danger:
-            Changing the returned tasks may lead to unexpected behavior, don't do it
-            unless the class explicitly documents it is safe to do so.
-        """
-
     @property
     @abc.abstractmethod
     def is_running(self) -> bool:
@@ -229,17 +216,8 @@ def unique_id(self) -> str:
         return self._unique_id
 
     @property
-    @override
     def tasks(self) -> collections.abc.Set[asyncio.Task[Any]]:
-        """The set of running tasks spawned by this service.
-
-        Users typically should not modify the tasks in the returned set and only use
-        them for informational purposes.
-
-        Danger:
-            Changing the returned tasks may lead to unexpected behavior, don't do it
-            unless the class explicitly documents it is safe to do so.
-        """
+        """The set of running tasks spawned by this service."""
         return self._tasks
 
     @property