Remove leftover Guardian mixin (#107424)

homeassistant/components/guardian/__init__.py

@@ -390,19 +390,12 @@ class PairedSensorEntity(GuardianEntity):
 
 
 @dataclass(frozen=True, kw_only=True)
-class ValveControllerEntityDescriptionMixin:
-    """Define an entity description mixin for valve controller entities."""
+class ValveControllerEntityDescription(EntityDescription):
+    """Describe a Guardian valve controller entity."""
 
     api_category: str
 
 
-@dataclass(frozen=True, kw_only=True)
-class ValveControllerEntityDescription(
-    EntityDescription, ValveControllerEntityDescriptionMixin
-):
-    """Describe a Guardian valve controller entity."""
-
-
 class ValveControllerEntity(GuardianEntity):
     """Define a Guardian valve controller entity."""