Remove parentheses.

Author: ZeroIntensity

peps/pep-9999.rst

@@ -53,7 +53,7 @@ proposal:
         return 2
 
     async def main():
-        result = (async yield from agenerator())
+        result = async yield from agenerator()
         assert result == 2
 
 
@@ -250,7 +250,7 @@ For example:
         return 2
 
     async def main():
-        result = (async yield from agenerator())
+        result = async yield from agenerator()
         print(result)  # 2