[rpc] remove missed rpc parameters

Summary:
Clean up RPC parameter mapping for estimatesmartpriority and estimatepriority,
which were removed in D1353 and D1350.

Test Plan:

make check && ./test/functional/test_runner.py

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix, jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1364