use unique_ptr (backport #3152)

[mergify]

---

This is an automatic backport of pull request #3152 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of ecfb739 has failed:

On branch mergify/bp/0.28.x/pr-3152
Your branch is up to date with 'origin/0.28.x'.

You are currently cherry-picking commit ecfb739e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   src/makernote_int.cpp
	modified:   src/makernote_int.hpp
	modified:   src/tiffcomposite_int.cpp
	modified:   src/tiffcomposite_int.hpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/tiffvisitor_int.cpp

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally