tests: Remove superfluous header guards in cpp files
Done with:
- for i in
rg -I -N --only-matching '#ifndef (.*_h)' --replace='$1' *cpp | xargs echo
; do unifdef -m -U $i *cpp; done - for i in
rg -I -N --only-matching '#define (.*_h)' --replace='$1' *cpp | xargs echo
; do sed -i "s/.*$i//g" *.cpp; done - pre-commit run --all-files