Remove direct bitcoin calls from qt/optionsdialog.cpp

Summary:
Partial backport of Core PR 10244
https://github.com/bitcoin/bitcoin/pull/10244/commits/90d4640b7eff3154a0750c5acb52d39bd41e0bbb
Progress towards T417

Test Plan:
ninja check
make check
bitcoin-qt # sanity checks; check options dialog

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D2871