C++ IR: Move ErrorExpr filter to TranslatedElement

The convention in the IR translation is to handle all ignored
expressions in this central place.

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -84,7 +84,13 @@ private predicate ignoreExprOnly(Expr expr) {
     // Ignore the allocator call, because we always synthesize it. Don't ignore
     // its arguments, though, because we use them as part of the synthesis.
     newExpr.getAllocatorCall() = expr
-  ) or
+  )
+  or
+  // The extractor deliberately emits an `ErrorExpr` as the first argument to
+  // the allocator call, if any, of a `NewOrNewArrayExpr`. That `ErrorExpr`
+  // should not be translated.
+  exists(NewOrNewArrayExpr new | expr = new.getAllocatorCall().getArgument(0))
+  or
   not translateFunction(expr.getEnclosingFunction())
   or
   // We do not yet translate destructors properly, so for now we ignore the

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -2866,13 +2866,6 @@ class TranslatedStmtExpr extends TranslatedNonConstantExpr {
 class TranslatedErrorExpr extends TranslatedSingleInstructionExpr {
   override ErrorExpr expr;
 
-  TranslatedErrorExpr() {
-    // The extractor deliberately emits an `ErrorExpr` as the first argument to
-    // the allocator call, if any, of a `NewOrNewArrayExpr`. That `ErrorExpr`
-    // should not be translated.
-    not exists(NewOrNewArrayExpr new | expr = new.getAllocatorCall().getArgument(0))
-  }
-
   override final Instruction getFirstInstruction() {
     result = getInstruction(OnlyInstructionTag())
   }