mtd: rawnand: tango: Remove the driver

The tango platform is getting removed [1], so the driver is no
longer needed.

[1] https://lore.kernel.org/linux-arm-kernel/20210120124812.2800027-1-arnd@kernel.org/T/

Cc: Marc Gonzalez <marc.w.gonzalez@free.fr>
Cc: Mans Rullgard <mans@mansr.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210120150555.1610132-1-arnd@kernel.org