test: run mempool_reorg.py even with wallet disabled

Summary:

- run mempool_reorg.py even when the wallet is not compiled
- add `locktime` argument to `create_self_transfer` and `send_self_transfer`
- use more logs instead of comments

Backport of core#21178.

Depends on D12434.

Note that in the source material the locktime is not passed down from
send_self_transfer to create_self_transfer which is an obvious oversight.
This is silently fixed in core#22210 but I also fixed it in this diff.

Test Plan:

./test/functional/test_runner.py mempool_reorg

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Subscribers: sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12435