mtd: core: Remove partid and partname debugfs files

partid and partname debugfs files were used just by SPI NOR, but they were
replaced by sysfs entries. Since these debugfs files are no longer used in
mtd, remove dead code. The directory is kept as it is used by nandsim,
mtdswap and docg3.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220225144656.634682-1-tudor.ambarus@microchip.com