[tests] Remove 'account' API from wallet_keypool_topup
Summary:
Removes usage of account API from the following functional tests:
- wallet_keypool_topup.py
Partial backport of Core PR13075
https://github.com/bitcoin/bitcoin/pull/13075/commits/5d536619abda745c298fd827a856df775f223241#diff-7e5918b156c945e8866cab6ee0b774d4
Test Plan:
test_runner.py wallet_keypool_topup
Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc
Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D4522