Revert "annotation_parens"

This reverts commit b6cd780453.

src/black/linegen.py

@@ -181,6 +181,9 @@ def visit_stmt(
 
     def visit_funcdef(self, node: Node) -> Iterator[Line]:
         """Visit function definition."""
+        if Preview.annotation_parens not in self.mode:
+            yield from self.visit_stmt(node, keywords={"def"}, parens=set())
+        else:
             yield from self.line()
 
             # Remove redundant brackets around return type annotation.

src/black/mode.py

@@ -149,6 +149,7 @@ def supports_feature(target_versions: Set[TargetVersion], feature: Feature) -> b
 class Preview(Enum):
     """Individual preview style features."""
 
+    annotation_parens = auto()
     long_docstring_quotes_on_newline = auto()
     string_processing = auto()