sharky leaks without a shard limit

[zelig]

sharky without shard limit (as implemented in https://github.com/ethersphere/bee/pull/2764) is unsound. Without limit, every time a shard is full, it is extended (slots process pop call). Because of variance this will always happen eventually, therefore shards will grow with use infinitely probably causing disk to fill up https://github.com/ethersphere/bee/issues/1258