* Transaction pool: Ensure that we prune transactions properly
There was a bug in the transaction pool that we didn't pruned
transactions properly because we called `prune_known`, instead of `prune`.
This bug was introduced by:
https://github.com/paritytech/substrate/pull/4629
This is required to have stale extrinsics being removed properly, so
that they don't fill up the tx pool.
* Fix compilation
* Fix benches
* ...