Remove log crate dependency
Instead we can use the `trace!` macro to log details about FFI calls. By
default, it's compiled out but the `ffi-trace` feature can be used to
enable it. These tracing printouts are only really useful for debugging
failures when writing scaffolding/bindings code.
Addresses #2224 - even disabled logging can have overhead depending with some backends, and
in very high frequency calls, generates unacceptable overhead and log-spam.
