Merge #9894: remove 'label' filter for rpc command help

Summary:
6665977 remove 'label' filter for rpc command help (Gregory Sanders)

Tree-SHA512: 0676c55b2893a469cd6785963affbb04126b9a32c130f1bb22dfd233ede6998f695187264e897ced4e0dac48451d9ae0311ebb4f7442096cad632fd22f75080e

Backport of Core PR9894
https://github.com/bitcoin/bitcoin/pull/9894/files

Test Plan:

make check
test_runner.py

Reviewers: jasonbcox, deadalnix, Fabien, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: jasonbcox, deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Subscribers: markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D3308