zram: Remove ZRAM_LOCK

The ZRAM_LOCK was used for locking and after the addition of spinlock_t
the bit set and cleared but there no reader of it.

Remove the ZRAM_LOCK bit.

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20240906141520.730009-3-bigeasy@linutronix.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>