Remove unused LockAssertion struct
Summary:
This is a backport of core#19979 [3/3]
https://github.com/bitcoin/bitcoin/pull/19979/commits/0bd1184adf6610c0bd14f4e9a25c0a200e65ae25
Depends on D10172
Test Plan: ninja all check-all
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10173