x11-fonts/afdko: Fix build with Clang 16 and remove the workaround

/wrkdirs/usr/ports/x11-fonts/afdko/work/afdko-3.9.6/c/shared/source/tx_shared/tx_shared.c:526:20: error: incompatible function pointer types assigning to 'size_t (*)(ctlStreamCallbacks *, void *, char **)' (aka 'unsigned long (*)(struct ctlStreamCallbacks_ *, void *, char **)') from 'size_t (ctlStreamCallbacks *, Stream *, char **)' (aka 'unsigned long (struct ctlStreamCallbacks_ *, Stream *, char **)') [-Wincompatible-function-pointer-types]
    h->cb.stm.read = stm_read;
                   ^ ~~~~~~~~
/wrkdirs/usr/ports/x11-fonts/afdko/work/afdko-3.9.6/c/shared/source/tx_shared/tx_shared.c:527:24: error: incompatible function pointer types assigning to 'size_t (*)(ctlStreamCallbacks *, void *, xmlDocPtr *)' (aka 'unsigned long (*)(struct ctlStreamCallbacks_ *, void *, struct _xmlDoc **)') from 'size_t (ctlStreamCallbacks *, Stream *, xmlDocPtr *)' (aka 'unsigned long (struct ctlStreamCallbacks_ *, Stream *, struct _xmlDoc **)') [-Wincompatible-function-pointer-types]
    h->cb.stm.xml_read = stm_xml_read;
                       ^ ~~~~~~~~~~~~
2 errors generated.