wallet: Remove deprecated OutputEligibleForSpending

Summary:
This is a partial backport of Core PR12257 : https://github.com/bitcoin/bitcoin/pull/12257/commits/43e04d13b1ffc02b1082176e87f420198b40c7b1

Depends on D3394

Test Plan:

make check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3396