test: run mempool_expiry.py even with wallet disabled
Summary:
Test coverage is also extended in this commit to: Ensure that another transaction in the mempool is not evicted when other transactions expire. Note: this other transaction does not have any ancestors in the mempool that expired. Otherwise it would be evicted from the mempool, and we already test this case.
Backport of core#20276.
Test Plan:
./test/functional/test_runner.py mempool_expiry
Reviewers: #bitcoin_abc, sdulfari
Reviewed By: #bitcoin_abc, sdulfari
Differential Revision: https://reviews.bitcoinabc.org/D12423