ECCVM/Translator: remove circuit size and log_circuit_size from MSGPACK

[iakovenkos]

My naive attempts to remove these fields from the MSGPACK in ECCVMFlavor led to breaking bb build, whereas it worked just fine in Translator. Probably removing those fields breaks some assumptions on the vk format. As they are fixed and not used as circuit witnesses, this should not be a security issue, but feels redundant.