[FRI] First FRI layer handling

[irakliyk]

Right now, we include first FRI layer into the FRI proof. This is redundant as the verifier can compute the values for the first FRI layer directly from trace and constraint queries. Removing first FRI layer from the proof should reduce of proof size roughly by 15%.

However, we can do this only when perfect zero knowledge is not required. When we implement ability to turn on perfect zero knowledge (via #9), we would need to include first FRI layer queries into the FRI proof. So, it probably makes sense to address this issue once #9 has been addressed.