staging: mt7621-mmc: Remove obsolete Kconfig flags

These values are not referred to anywhere else in the kernel. Card
detect is controlled by the device tree property "mediatek,cd-poll",
and there is no driver support for eMMC whatsoever.

Signed-off-by: George Hilliard <thirtythreeforty@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>