Change UniquePtr to std::unique_ptr

UniquePtr.h in libnativehelper/include is deprecated and will be removed
soon. Switching to the standard std::unique_ptr.

Bug: 63686260
Test: builds, cmd works in the device.
Change-Id: Ib008acd1dd7dba2305b0797c9dc7bab1aa747e7d
1 file changed