Fix rpc_deprecated with wellington activated

Summary: The test expects a statistics that will no longer be present after wellington activated.

Test Plan:
Rebase upon https://reviews.bitcoinabc.org/D13171:

./test/functional/test_runner.py --with-wellingtonactivation rpc_deprecated

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13180