Summary: stop using the gArgs wrappers

Summary:

• Scripted diff, checked manually:

find src/ -name "*.cpp" ! -wholename "src/util.h" ! -wholename "src/util.cpp" | xargs perl -i -pe 's/(?<!\.)(ParseParameters|ReadConfigFile|IsArgSet|(Soft|Force)?(Get|Set)(|Bool|)Arg(s)?)\(/gArgs.\1(/g'

• remove unused gArgs wrappers

Backport from Core's https://github.com/bitcoin/bitcoin/commit/c2704ec98a1b7b35b6a7c1b6b26a3f16d44e8880

Fixes T212

Test Plan:

make check && test/functional/test_runner.py

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix, teamcity

Maniphest Tasks: T212

Differential Revision: https://reviews.bitcoinabc.org/D1044