docs: mtd: spi-nor: drop obsolete info

The architecture description is obsolete, it no longer applies to
the current SPI NOR framework state, remove it.

Reviewed-by: Michael Walle <michael@walle.cc>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Link: https://lore.kernel.org/r/20231124184902.1194235-3-tudor.ambarus@linaro.org


Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>