This change removes both the member function swap and the free function overload of swap for std::span. While swap is a member and overloaded for every other container in the standard library [1], it is neither a member function nor a free function overload for std::span [2]. Thus the corresponding implementation should be removed.
[1] https://eel.is/c++draft/libraryindex#:swap
[2] https://eel.is/c++draft/span.overview