DOC: Fix warning directive and adjust BooleanDtype docstring attributes (fixes #61939)

Author: Poorvinfi

pandas/core/arrays/boolean.py

@@ -77,7 +77,6 @@ class BooleanDtype(BaseMaskedDtype):
     --------
     Create a Series with BooleanDtype:
 
-    >>> import pandas as pd
     >>> s = pd.Series([True, False, None], dtype='boolean')
     >>> s
     0     True