Remove unused variables.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Rename sum -> _sum.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Move `use` statements.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>