Since setup_regulators variant function is not used by any vendors, simply
remove it.

Link: https://lore.kernel.org/r/20201205120041.26869-2-stanley.chu@mediatek.comReviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>