mmc_da: garbage-collect sdda_get_max_data

The function is unused since 5aedb8b1d4a6.

For information, in MMC CAM both XPT_GET_TRAN_SETTINGS and XPT_PATH_INQ
obtain data using MMC_SIM_GET_TRAN_SETTINGS. So, "overlapping"
information like ccb_trans_settings_mmc::host_max_data and
ccb_pathinq::maxio is derived from the same source.
That's why sdda_get_max_data was redundant.

Reported by: bz
MFC after: 5 days