[tests] Remove 'account' API from wallet_import_rescan

Summary:
Removes usage of account API from the following functional tests:

• wallet_import_rescan.py

Partial backport of Core PR13075
https://github.com/bitcoin/bitcoin/pull/13075/commits/5d536619abda745c298fd827a856df775f223241#diff-41ca09babe91abee6c9f1bf338709ecc

Test Plan:

test_runner.py wallet_import_rescan

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4521