The DelegationBuilder does not need a complete proof to build a delegation, only its master public key and its limited proof id. Add a constructor that does not require the proof.
Remove also the proofid member that can be computed from the limited ID.
Replace the `DelegationBuilder::importDelegation` method with a `DelegationBuilder(const Delegation &dg)` constructor.
Use these 2 new constructors in the `delegateavalancheproof` RPC.