mtd: rawnand: remove ->legacy.erase and single_erase()

Now that the last user of this hook, denali.c, stopped using it,
we can remove the erase hook from nand_legacy.

I squashed single_erase() because only the difference between
single_erase() and nand_erase_op() is the number of bit shifts.

The status/ret conversion in nand_erase_nand() is unneeded since
commit eb94555e9e ("mtd: nand: use usual return values for the
->erase() hook"). Cleaned it up now.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

include/linux/mtd/rawnand.h

@@ -927,7 +927,6 @@ static inline void nand_controller_init(struct nand_controller *nfc)
  * @waitfunc: hardware specific function for wait on ready.
  * @block_bad: check if a block is bad, using OOB markers
  * @block_markbad: mark a block bad
- * @erase: erase function
  * @set_features: set the NAND chip features
  * @get_features: get the NAND chip features
  * @chip_delay: chip dependent delay for transferring data from array to read
@@ -953,7 +952,6 @@ struct nand_legacy {
 	int (*waitfunc)(struct nand_chip *chip);
 	int (*block_bad)(struct nand_chip *chip, loff_t ofs);
 	int (*block_markbad)(struct nand_chip *chip, loff_t ofs);
-	int (*erase)(struct nand_chip *chip, int page);
 	int (*set_features)(struct nand_chip *chip, int feature_addr,
 			    u8 *subfeature_para);
 	int (*get_features)(struct nand_chip *chip, int feature_addr,