It is no longer used by anything inside libbitcoinkernel, move it to
node/mempool_persist_args.h where it belongs.
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/25487 | core#25487]]
https://github.com/bitcoin/bitcoin/pull/25487/commits/aa306765419f7dbea12b12e15553039835ba0e4d
Depends on D15722