Fix description in Python 3.7 What's New (#3603)

Author: paulromano

Doc/whatsnew/3.7.rst

@@ -296,9 +296,8 @@ Optimizations
   (Contributed by Serhiy Storchaka in :issue:`24821`.)
 
 * Fast implementation from standard C library is now used for functions
-  :func:`~math.tgamma`, :func:`~math.lgamma`, :func:`~math.erf` and
-  :func:`~math.erfc` in the :mod:`math` module. (Contributed by Serhiy
-  Storchaka in :issue:`26121`.)
+  :func:`~math.erf` and :func:`~math.erfc` in the :mod:`math` module.
+  (Contributed by Serhiy Storchaka in :issue:`26121`.)
 
 * The :func:`os.fwalk` function has been sped up by 2 times.  This was done
   using the :func:`os.scandir` function.