Weighted Adder unused ancilla for mct

[ankprd]

Information

• Qiskit Terra version: 0.23.0
• Python version: 3
• Operating system: Ubuntu

What is the current behavior?

WeightedAdder implementation uses mct with default mode 'no-ancilla' but allocates an ancilla qubit for it
(similar to #4786)

Steps to reproduce the problem

What is the expected behavior?

Either use mct(mode = 'v-chain') or not allocating qr_control (and not passing it to mct), l.265 and 284 of https://github.com/Qiskit/qiskit-terra/blob/master/qiskit/circuit/library/arithmetic/weighted_adder.py
(as it is, the resulting circuit has one unused qubit)

Suggested solutions