Switch aidl::nullable to std::optional

AIDL's @nullable is represented as std::optional in C++ backend.
The previous aidl::nullable was a temporary solution to avoid
merge-conflicts between rvc-dev and master branches.

Bug: 151275535
Test: m
Change-Id: I8fe5bfc1763087e7ff364b4408f862436492d1db
diff --git a/services/incremental/IncrementalService.cpp b/services/incremental/IncrementalService.cpp
index a5f0d04..f7082a9 100644
--- a/services/incremental/IncrementalService.cpp
+++ b/services/incremental/IncrementalService.cpp
@@ -23,7 +23,6 @@
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <binder/AppOpsManager.h>
-#include <binder/Nullable.h>
 #include <binder/Status.h>
 #include <sys/stat.h>
 #include <uuid/uuid.h>
@@ -1404,7 +1403,7 @@
     }
 
     FileSystemControlParcel fsControlParcel;
-    fsControlParcel.incremental = aidl::make_nullable<IncrementalFileSystemControlParcel>();
+    fsControlParcel.incremental = std::make_optional<IncrementalFileSystemControlParcel>();
     fsControlParcel.incremental->cmd.reset(dup(ifs.control.cmd()));
     fsControlParcel.incremental->pendingReads.reset(dup(ifs.control.pendingReads()));
     fsControlParcel.incremental->log.reset(dup(ifs.control.logs()));