Remove Commitment template parameter for flavor-specific Transcripts

[lucasxia01]

Currently, the flavor-specific Transcripts, which define the structure of a transcript and provide serialization/deserialization functions, are parameterized by Commitment to generalize to the recursive case, which is wrong. They should be parameterized by all types in this case. However, since uint32_t is represented as a field_t<Builder>, this doesn't work, so I think we should just duplicate this class.