mtd: maps: remove dead select of MTD_CFI_BE_BYTE_SWAP

'select' does not work on config options in a 'choice', so currently it is
possible to enable MTD_PHYSMAP_IXP4XX without MTD_CFI_BE_BYTE_SWAP.

From a previous conversation, it was decided to remove the select entirely:
https://lore.kernel.org/all/c6268184-4904-49d9-b14f-0e11dce8bdad@app.fastmail.com/

This dead select was found by kconfirm, a static analysis tool for Kconfig.

Signed-off-by: Julian Braha <julianbraha@gmail.com>
Link: $URL [1]"
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>