idmap2: fix clang-tidy warnings [modernize-*]

Bug: 120024673
Test: mmm frameworks/base/cmds/idmap2; check output
Change-Id: I8768169fb7b541eb6b1aa3311c46a710eb71aac9
diff --git a/cmds/idmap2/idmap2d/Idmap2Service.cpp b/cmds/idmap2/idmap2d/Idmap2Service.cpp
index 7b16093..d2e46e1 100644
--- a/cmds/idmap2/idmap2d/Idmap2Service.cpp
+++ b/cmds/idmap2/idmap2d/Idmap2Service.cpp
@@ -56,8 +56,7 @@
 
 }  // namespace
 
-namespace android {
-namespace os {
+namespace android::os {
 
 Status Idmap2Service::getIdmapPath(const std::string& overlay_apk_path,
                                    int32_t user_id ATTRIBUTE_UNUSED, std::string* _aidl_return) {
@@ -132,9 +131,8 @@
     return error("failed to write to idmap path " + idmap_path);
   }
 
-  _aidl_return->reset(new std::string(idmap_path));
+  *_aidl_return = std::make_unique<std::string>(idmap_path);
   return ok();
 }
 
-}  // namespace os
-}  // namespace android
+}  // namespace android::os