The following have zero references repo-wide:
Move::to_sq_unchecked() (types.h): added in 542c30c2 for a
branchless correction-history update; its only caller was removed
in 5ae13d2b ("Remove Redundant Branchless Execution"), leaving the
method unused.
PipeDeleter (misc.h): the custom deleter for the std::unique_ptr<FILE,
PipeDeleter> that wrapped popen("lscpu"). That pipe was removed in
c8375c2f ("On linux use sysfs instead of lscpu"), so the struct has
been unused since.
Dropping PipeDeleter also removes the last user of <cstdio> in misc.h, so that include is dropped as well.
closes https://github.com/official-stockfish/Stockfish/pull/6948
No functional change
