Don't store proofs in EL blocks

[gballet]

This is a tracker issue for a potential improvement.

Storing proofs in blocks is redundant as they have to be stored in CL blocks. Furthermore, they are added to the EL block, but are not part of the hash. It makes sense not to store them in the EL block, and pass it to the ExecutionPayload via an interface change.

[gballet]

long done, closing