mtd: rawnand: denali: remove ->erase hook

Commit f9ebd1bb

 ("mtd: rawnand: Deprecate ->erase()") discouraged
the use of this hook, so I am happy to follow the suggestion.

Although the Denali IP provides a special MAP10 command for erasing,
using it would not buy us much. The Denali IP actually works with the
generic erasing by single_erase() + ->cmdfunc hook (nand_command_lp)
+ ->cmd_ctrl hook (denali_cmd_ctrl).

This method is also deprecated, but denali_erase() can go away
irrespective of ->exec_op conversion.

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>