Make import tests in wallet_listtransactions.py legacy wallet only

Summary:
Existing import* RPCs are disabled for descriptor wallets, so only do
these tests for legacy wallets.

This is a backport of core#18788 [3/16]
https://github.com/bitcoin/bitcoin/pull/18788/commits/553dbf9af4dea96e6a3e79bba9607003342029bd

Test Plan: test/functional/test_runner.py wallet_listtransactions

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10655