Dead code removal

Summary:

• benchmark: Removed bench/perf.cpp
• node: Removed unused wallet-related methods from the Node interface.

This is a backport of Core PR13025

Test Plan:

make check
make bench

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D3349