Remove BucketListSize from Soroban RPC code base

[dmkozh]

The new version of soroban-simulation crate (integrated in #92) encapsulates the bucket list size determination logic, so there is no longer need to pass it to the simulation functions. Thus all the plumbing can be removed. When RPC stops using it, the bucket list size field can be safely removed from tx meta (as there shouldn't be any more users of this field).