Commit c0e5f4e7 ("misc: rtsx: Add support for RTS5261") silently
removed RTSX_MS_CARD from its MFD cell, so rtsx_pci_ms isn't used
by any driver anymore.

Since there doesn't seem to any complaint, hence drop the driver.
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Link: https://lore.kernel.org/r/20240620031159.142637-1-kai.heng.feng@canonical.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>