mtd: kill the nand_ecclayout struct

Now that all MTD drivers have moved to the mtd_ooblayout_ops model we can
safely remove the struct nand_ecclayout definition, and all the remaining
places where it was still used.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

include/uapi/mtd/mtd-abi.h

@@ -228,7 +228,7 @@ struct nand_oobfree {
  * complete set of ECC information. The ioctl truncates the larger internal
  * structure to retain binary compatibility with the static declaration of the
  * ioctl. Note that the "MTD_MAX_..._ENTRIES" macros represent the max size of
- * the user struct, not the MAX size of the internal struct nand_ecclayout.
+ * the user struct, not the MAX size of the internal OOB layout representation.
  */
 struct nand_ecclayout_user {
 	__u32 eccbytes;