bpo-30273: Update sysconfig (#1464)

The AST_H_DIR variable was removed from Makefile.pre.in by the commit
a5c62a8e9f0de6c4133825a5710984a3cd5e102b (bpo-23404).

AST_H_DIR was hardcoded to "Include", so replace the removed variable
by its content.

Remove also ASDLGEN variable from sysconfig example since this
variable was also removed.
2 files changed