JS: Simplify type hierarchy for SourceNode

javascript/ql/lib/semmle/javascript/dataflow/Sources.qll

@@ -33,13 +33,7 @@ private import semmle.javascript.internal.CachedStages
  * import("fs")
  * ```
  */
-class SourceNode extends DataFlow::Node {
-  SourceNode() {
-    this instanceof SourceNode::Range
-    or
-    none() and this instanceof SourceNode::Internal::RecursionGuard
-  }
-
+class SourceNode extends DataFlow::Node instanceof SourceNode::Range {
   /**
    * Holds if this node flows into `sink` in zero or more local (that is,
    * intra-procedural) steps.
@@ -340,12 +334,6 @@ module SourceNode {
       DataFlow::functionReturnNode(this, _)
     }
   }
-
-  /** INTERNAL. DO NOT USE. */
-  module Internal {
-    /** An empty class that some tests are using to enforce that SourceNode is non-recursive. */
-    abstract class RecursionGuard extends DataFlow::Node { }
-  }
 }
 
 private class NodeModuleSourcesNodes extends SourceNode::Range {