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.lock

@@ -3,11 +3,12 @@
 [[package]]
 name = "wasi-nn"
 version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c909acded993dc129e02f64a7646eb7b53079f522a814024a88772f41558996"
 
 [[package]]
 name = "wasi-nn-example"
 version = "0.19.0"
 dependencies = [
- "wasi-nn 0.1.0",
+ "wasi-nn",
 ]
-