scripted-diff: Remove g_rpc_node references

Summary:

This commit does not change behavior

-BEGIN VERIFY SCRIPT-
git grep -l g_rpc_node | xargs sed -i 's/g_rpc_node->/node./g'
-END VERIFY SCRIPT-

Partial backport of core PR18740:
https://github.com/bitcoin/bitcoin/pull/18740/commits/ccb5059ee89f6e8dc31ba5b82830b384890bb65e

Depends on D7990.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7991