[backport#17405] wallet: Remove unused boost::this_thread::interruption_point

Summary:
fad1de66a29bf6bd348a932150dad7d472feb3d0 wallet: Remove unused boost::this_thread::interruption_point (MarcoFalke)

Pull request description:

`BerkeleyEnvironment::Open` is only called from the main thread (init) or an http rpc thread, neither of which can be interrupted, so remove the useless interruption point.

`BerkeleyEnvironment{}` is only used in tests, which run in a single process/thread, so remove the useless interruption point.

Backport of Core PR17405

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7709