power: supply: ab8500: Remove unused struct ab8500_chargalg_sysfs_entry

After commit 75ee3f6f("power: supply: ab8500_chargalg: Drop enable/disable
sysfs"), no one use struct ab8500_chargalg_sysfs_entry, so remove it.

Signed-off-by: Yuan Can <yuancan@huawei.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>