rename schnorr functional test (rename-only)
Summary:
In D3253 this was kept the same name to aid in diff detection, time to
rename it.
Test Plan: test_runner.py
Reviewers: deadalnix, jasonbcox, Mengerian, #bitcoin_abc
Reviewed By: jasonbcox, Mengerian, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D3415