UPSTREAM: zram: remove unused SECTOR_SIZE define

(cherry-pick from commit a830eff749eb2bf906783f6bf74a74dad3de3aea)

Drop SECTOR_SIZE define, because it's not used.

Bug: 25951511

Change-Id: I5f38ff27532f452873386266f56126f61585e353
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Weijie Yang <weijie.yang@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>