Finish conversion of rpc to use pushKV

Summary: As per title. Fixes missed changes from D1990.

Test Plan:

make VERBOSE=1 check && ./test/functional/test_runner.py

Reviewers: #bitcoin_abc, deadalnix, schancel

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: Fabien, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D2064