Remove 'Not implemented for Series' from _num_doc in generic.py (pandas-dev#58096)

Documentation fix in `generic.py`
line 11715: Removed 'Not implemented for Series' in _num_doc given that `numeric_only` is now implemented for Series in all the methods min, max, mean, median, skew, kurt

Author: kamelCased

pandas/core/generic.py

@@ -11718,7 +11718,7 @@ def last_valid_index(self) -> Hashable:
 skipna : bool, default True
     Exclude NA/null values when computing the result.
 numeric_only : bool, default False
-    Include only float, int, boolean columns. Not implemented for Series.
+    Include only float, int, boolean columns.
 
 {min_count}\
 **kwargs