DOC: remove links to deprecated methods (pandas-dev#46700)

Author: guoci

pandas/core/reshape/concat.py

@@ -215,8 +215,6 @@ def concat(
 
     See Also
     --------
-    Series.append : Concatenate Series.
-    DataFrame.append : Concatenate DataFrames.
     DataFrame.join : Join DataFrames using indexes.
     DataFrame.merge : Merge DataFrames by indexes or columns.