Rust: Remove remaining DefinitionExt references.

rust/ql/lib/codeql/rust/dataflow/internal/SsaImpl.qll

@@ -330,33 +330,6 @@ private module Cached {
 import Cached
 private import codeql.rust.dataflow.Ssa
 
-/**
- * An extended static single assignment (SSA) definition.
- *
- * This is either a normal SSA definition (`Definition`) or a
- * phi-read node (`PhiReadNode`).
- *
- * Only intended for internal use.
- */
-class DefinitionExt extends Impl::DefinitionExt {
-  CfgNode getARead() { result = getARead(this) }
-
-  override string toString() { result = this.(Ssa::Definition).toString() }
-
-  override Location getLocation() { result = this.(Ssa::Definition).getLocation() }
-}
-
-/**
- * A phi-read node.
- *
- * Only intended for internal use.
- */
-class PhiReadNode extends DefinitionExt, Impl::PhiReadNode {
-  override string toString() { result = "SSA phi read(" + this.getSourceVariable() + ")" }
-
-  override Location getLocation() { result = Impl::PhiReadNode.super.getLocation() }
-}
-
 private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInputSig {
   class Expr extends CfgNodes::AstCfgNode {
     predicate hasCfgNode(SsaInput::BasicBlock bb, int i) { this = bb.getNode(i) }