Finish PR14987 and clean up some functions

Summary:
Removes now unnecessary functions, etc. from the portioned backporting
of PR14987.

Depends on D5291, D5290, D5919, D5916, D5914, D5913, D5899

Test Plan:
On master:

ninja
./bitcoind
./bitcoin-cli help > RPCs
./getrpchelps.sh RPCs master

Then on the patched branch:

ninja
./bitcoind
./getrpchelps.sh RPCs patched
./checkrpc.sh RPCs master patched finish.diff

Verify finish.diff does not exist.

Scripts:

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5922