wasi-nn: use the newly-published Rust bindings for wasi-nn

The bindings are now published on [crates.io](https://crates.io/crates/wasi-nn) and have been moved to their [own repository](https://github.com/bytecodealliance/wasi-nn).

crates/wasi-nn/examples/classification-example/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 publish = false
 
 [dependencies]
-wasi-nn = { path = "../wasi-nn-rust-bindings", version = "0.1.0" }
+wasi-nn = "0.1.0"
 
 # This crate is built with the wasm32-wasi target, so it's separate
 # from the main Wasmtime build, so use this directive to exclude it