DOC: Remove redundant word from Categorical docstring (#51094)

Remove redundant word from `Categorical` docstring

Author: dpoznik

pandas/core/arrays/categorical.py

@@ -248,7 +248,7 @@ class Categorical(NDArrayBackedExtensionArray, PandasObject, ObjectStringArrayMi
     """
     Represent a categorical variable in classic R / S-plus fashion.
 
-    `Categoricals` can only take on only a limited, and usually fixed, number
+    `Categoricals` can only take on a limited, and usually fixed, number
     of possible values (`categories`). In contrast to statistical categorical
     variables, a `Categorical` might have an order, but numerical operations
     (additions, divisions, ...) are not possible.