pythongh-145998: Remove duplicated "What's New in 3.15" entry (python#145994)

Author: ShaharNaveh

Doc/whatsnew/3.15.rst

@@ -1014,13 +1014,6 @@ symtable
   (Contributed by Yashp002 in :gh:`143504`.)
 
 
-symtable
---------
-
-* Add :meth:`symtable.Function.get_cells` and :meth:`symtable.Symbol.is_cell` methods.
-  (Contributed by Yashp002 in :gh:`143504`.)
-
-
 sys
 ---