Remove power hugging formatting from preview (#2928)

It is falsely placed in preview features and always formats the power operators, it was added in #2789 but there is no check for formatting added along with it.

src/black/mode.py

@@ -127,7 +127,6 @@ class Preview(Enum):
     """Individual preview style features."""
 
     string_processing = auto()
-    hug_simple_powers = auto()
 
 
 class Deprecated(UserWarning):
@@ -163,7 +162,9 @@ def __contains__(self, feature: Preview) -> bool:
         """
         if feature is Preview.string_processing:
             return self.preview or self.experimental_string_processing
-        return self.preview
+        # TODO: Remove type ignore comment once preview contains more features
+        #  than just ESP
+        return self.preview  # type: ignore
 
     def get_cache_key(self) -> str:
         if self.target_versions: