[qt] send: Clear All also resets coin control options

Summary:
This change makes it so that a custom change address and manual input selection are removed if the user clicks Clear All in the send screen.

Backport of Bitcoin Core PR12432
https://github.com/bitcoin/bitcoin/pull/12432

Test Plan:

1. Start BitcoinABC wallet: ./src/qt/bitcoin-qt -regtest
2. Enable the check named Enable coin control features, at Settings -> Options -> Wallet.
3. Go to Send dialog.
4. Enable the check Custom change address and fill with one address at the right.
5. Click on Clear all button.
6. Verify that the checkbox and the Custom change address text are cleaned.

Reviewers: Fabien, #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4078