Update wallet_listsinceblock.py to use signrawtransactionwithwallet rpc

Summary:
This has been added before D2009 gets landed, it needs to be updated as
signrawtransaction is going to get deprecated in favor of
signrawtransactionwithwallet and signrawtransactionwithkey.

Test Plan:

./test/functional/test_runner.py wallet_listsinceblock

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: schancel

Differential Revision: https://reviews.bitcoinabc.org/D2763