bpo-35177, Python-ast.h: Fix "Yield" compiler warning (GH-10664)

Partially revert commit 5f2df88b63e50d23914e97ec778861a52abdeaad:
add "#undef Yield" to .c files after including Python-ast.h.

Fix the warning:

    winbase.h(102): warning C4005: 'Yield': macro redefinition
diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 1bf822c..2d5dc88 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -11,6 +11,7 @@
 #include "Python.h"
 
 #include "Python-ast.h"
+#undef Yield   /* undefine macro conflicting with <winbase.h> */
 #include "pycore_pystate.h"
 #include "grammar.h"
 #include "node.h"