I think not. Because it’s not indexing the result page:
See:
<?php if (is_search()) { ?>
if is Search doesn’t index or follow the page (for example to not show duplicated content). But you can remove the code if you feel you are losing views.
I was reading an article about this. Even if WordPress doesn’t generate the /s=X page automatically, some plugins or even users can generate.
My recommendation is to keep the code.