mtd: remove unused header file <linux/mtd/latch-addr-flash.h>

Commit d24dbd75 ("mtd: maps: Get rid of the latch-addr-flash driver")
removed the last user of <linux/mtd/latch-addr-flash.h> but left the header
file behind.  Nothing uses this file, delete it now.

Cc: Boris Brezillon <bbrezillon@kernel.org>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211102220203.940290-7-corbet@lwn.net