fixup lifetime

Author: llucax

src/frequenz/client/microgrid/_lifetime.py

@@ -37,14 +37,7 @@ def __post_init__(self) -> None:
             raise ValueError("Start must be before or equal to end.")
 
     def active_at(self, timestamp: datetime) -> bool:
-        """Check whether this lifetime is active at a specific timestamp.
-
-        Args:
-            timestamp: The timestamp to check activity for.
-
-        Returns:
-            True if active at the given timestamp, False otherwise.
-        """
+        """Check whether this lifetime is active at a specific timestamp."""
         if self.start is not None and self.start > timestamp:
             return False
         if self.end is not None: