[Feature] Remove is_dummy from Record struct and add implicit inner circuit enforcement

[howardwu]

🚀 Feature

Remove is_dummy from Record struct and add implicit inner circuit enforcement. We can also forgo encoding and encrypting it into encrypted records - note that this doesn't change the encrypted record size, however it should ever so slightly decrease the constraint count of the inner circuit. However, the added enforcement of is_dummy is accrued in the inner circuit (but we should be doing this check).

Motivation

(Outline your motivation here)

Implementation

Are you willing to open a pull request? (See CONTRIBUTING)

[raychu86]

Relevant issue - https://github.com/AleoHQ/snarkOS/issues/343.

[howardwu]

Also, we should rename this check to is_noop.

[howardwu]

This change will improve the record_commitment constraint cost and native size cost. We currently allocate the bit as a byte and pay for 1 extra byte wherever this record_commitment is checked.

[Pratyush]

This enables differentiating between normal transactions and transactions that use dummy records, no?

[howardwu]

Closing as dummy records will no longer be necessary with design changes.