gui: Remove unused interfaces::Node references

Summary:

Remove Node references no longer needed after previous commit

Partial backport (2/4) of bitcoin-core/gui PR35:
https://github.com/bitcoin-core/gui/pull/35/commits/91aced7c7e6e75c1f5896b7e3843015177f32748

Depends on D8653.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8654