Don't include desugared nodes in the printed AST

The base `PrintAstConfiguration` class already has a predicate for
filtering out desugared nodes - this change just makes use of it in the
query.

This fixes https://github.com/github/codeql-team/issues/408, which was
caused by including nodes representing the desugaring of

    a[b] = c

in the query output. This would result in multiple edges to the same
target node (one from the surface AST and another from the desugared
AST), which the VSCode AST viewer cannot handle.

ql/src/ide-contextual-queries/printAst.ql

@@ -21,6 +21,7 @@ external string selectedSourceFile();
  */
 class Cfg extends PrintAstConfiguration {
   override predicate shouldPrintNode(AstNode n) {
+    super.shouldPrintNode(n) and
     n.getLocation().getFile() = getFileBySourceArchiveName(selectedSourceFile())
   }
 }