Drop `for_current_target_` from `Importer::class_template_instantiations_`.

The renamed field includes decls from *all* targets, because
`IsFromCurrentTarget` *always* returns true for
`ClassTemplateSpecializationDecl`s, since `GetOwningTarget` has the
following code:

```
BazelLabel Importer::GetOwningTarget(const clang::Decl* decl) const {
  // Template instantiations need to be generated in the target that
  // triggered the instantiation (not in the target where the template
  // is defined).
  if (IsFullClassTemplateSpecializationOrChild(decl)) {
    return invocation_.target_;
  }
```

PiperOrigin-RevId: 476224525
diff --git a/rs_bindings_from_cc/importer.cc b/rs_bindings_from_cc/importer.cc
index aa1ab56..f609c9c 100644
--- a/rs_bindings_from_cc/importer.cc
+++ b/rs_bindings_from_cc/importer.cc
@@ -411,8 +411,8 @@
 std::vector<ItemId> Importer::GetOrderedItemIdsOfTemplateInstantiations()
     const {
   std::vector<SourceLocationComparator::OrderedItemId> items;
-  items.reserve(class_template_instantiations_for_current_target_.size());
-  for (const auto* decl : class_template_instantiations_for_current_target_) {
+  items.reserve(class_template_instantiations_.size());
+  for (const auto* decl : class_template_instantiations_) {
     items.push_back({GetSourceOrderKey(decl), GenerateItemId(decl)});
   }
 
@@ -664,7 +664,7 @@
 
   // Store `specialization_decl`s so that they will get included in
   // IR::top_level_item_ids.
-  class_template_instantiations_for_current_target_.insert(specialization_decl);
+  class_template_instantiations_.insert(specialization_decl);
 
   return ConvertTypeDecl(specialization_decl);
 }