DOC: Remove reference to PyArray_MultiIter_SIZE. (#19976)
DOC: Remove reference to PyArray_MultiIter_SIZE. (#19976)

Remove docs reference to non-existent C macro
charris/numpy,numpy/numpy,numpy/numpy,jakirkham/numpy,pdebuyl/numpy,seberg/numpy,anntzer/numpy,seberg/numpy,anntzer/numpy,mhvk/numpy,endolith/numpy,jakirkham/numpy,pdebuyl/numpy,pdebuyl/numpy,mattip/numpy,mhvk/numpy,mattip/numpy,mattip/numpy,endolith/numpy,jakirkham/numpy,seberg/numpy,charris/numpy,rgommers/numpy,jakirkham/numpy,mhvk/numpy,mhvk/numpy,anntzer/numpy,jakirkham/numpy,charris/numpy,charris/numpy,seberg/numpy,pdebuyl/numpy,anntzer/numpy,endolith/numpy,rgommers/numpy,mhvk/numpy,mattip/numpy,numpy/numpy,endolith/numpy,rgommers/numpy,numpy/numpy,rgommers/numpy