Change CheckMembership opcode to ComputeRoot

[kevaundray]

Problem

Currently, the check membership opcode will compute the merkle root and then add an Eq constraint. The Eq constraint can be computed in Noir.

Solution

Change CheckMembership Opcode to MerkleComputeRoot instead.

Alternatives considered

(Describe any alternative solutions you have considered.)

Additional context

(If applicable.)

[kevaundray]

This also requires an change in the acvm repo and all of the backends, so should be done sooner rather than later

[TomAFrench]

Resolved in #233