scanner_init/scanner_finish weren't actually called from anywhere,
and the scanbuf variables they set up weren't used either.

Remove unused declaration for mm_realloc, too.

John Naylor

Discussion: https://postgr.es/m/CAJVSVGWGqY9YBs2EwtRUkbNv=hXkN8yRPOoD1wxE6COgvvrz5g@mail.gmail.com