DOC: Remove alias for numpy.random.randn from the docs (pandas-dev#28082)

Author: WuraolaOyewusi

doc/source/conf.py

@@ -315,7 +315,6 @@
    import numpy as np
    import pandas as pd
 
-   randn = np.random.randn
    np.random.seed(123456)
    np.set_printoptions(precision=4, suppress=True)
    pd.options.display.max_rows = 15

doc/source/whatsnew/v0.10.0.rst

@@ -498,7 +498,7 @@ Here is a taste of what to expect.
 
 .. code-block:: ipython
 
-  In [58]: p4d = Panel4D(randn(2, 2, 5, 4),
+  In [58]: p4d = Panel4D(np.random.randn(2, 2, 5, 4),
     ....:       labels=['Label1','Label2'],
     ....:       items=['Item1', 'Item2'],
     ....:       major_axis=date_range('1/1/2000', periods=5),