[feat] Utreexo: removing item from the accumulator

[m-kus]

Context

Utreexo is a hash based accumulator that enables compact UTXO set representation and efficient updates.
For every transaction input we remove one item (leaf) from the virtual Utreexo forest, and update the accumulator which consists of tree roots and total number of leaves.
For every transaction output we add one item (leaf) to the Utreexo forest thus again updating the accumulator.

Task

Implement UtreexoAccumulatorImpl::delete

Materials

• https://eprint.iacr.org/2019/611.pdf (Algorithm 2: DeleteOne)
• community call https://www.youtube.com/watch?v=jq6cx6LowkA