ref(anyhow): Disable anyhow's backtrace feature

Since anyhow 1.0.77, backtrace feature is not needed for
Rust 1.65+ (https://github.com/dtolnay/anyhow/releases/tag/1.0.77).
Because sentry has a higher MSRV than that, it's no longer necessary
to enable this feature.

Author: sugar700