Revert "Use aidl::nullable for nullable type in C++"

Revert submission 10632869-nullable-compat-rvc-dev-plus-aosp

Reason for revert: incorrect merged-in line
Reverted Changes:
I33822bc76:Use aidl::nullable for nullable type in C++
I378dbf848:Add aidl::nullable type for nullable in AIDL

Change-Id: I98d4041770fe97b622aaaf8c829b97259bd82e2c
Exempt-From-Owner-Approval: revert wrong submission
diff --git a/cmds/idmap2/idmap2d/Idmap2Service.h b/cmds/idmap2/idmap2d/Idmap2Service.h
index b6f5136..047353f 100644
--- a/cmds/idmap2/idmap2d/Idmap2Service.h
+++ b/cmds/idmap2/idmap2d/Idmap2Service.h
@@ -19,7 +19,9 @@
 
 #include <android-base/unique_fd.h>
 #include <binder/BinderService.h>
-#include <binder/Nullable.h>
+
+#include <optional>
+#include <string>
 
 #include "android/os/BnIdmap2.h"
 
@@ -44,7 +46,7 @@
   binder::Status createIdmap(const std::string& target_apk_path,
                              const std::string& overlay_apk_path, int32_t fulfilled_policies,
                              bool enforce_overlayable, int32_t user_id,
-                             aidl::nullable<std::string>* _aidl_return) override;
+                             std::optional<std::string>* _aidl_return) override;
 };
 
 }  // namespace android::os