Destructuring a tuple emits `inc_rc` instructions for all arrays even if assigned to `_`

[TomAFrench]

Consider the below program

unconstrained fn main(b: ([Field; 2], Field)) {
    let (_, _) = b;
}

We destructure b but immediately discard the destructured internals so this is a noop. We would then expect this program to be completely empty.

The initial SSA generated however is the below

After Initial SSA:
brillig(inline) fn main f0 {
  b0(v0: [Field; 2], v1: Field):
    inc_rc v0
    return
}

We're then unnecessarily increasing the reference counter for v0 such that we'll never benefit from the optimisations from the case where rc == 1