Remove implementation_from_dafny.rs from git (#523)

We aren't patching these files any more, and the rust tests current fail in the nightly build because the latest on the `feat-rust` branch changes the output.

Dry run of nightly build on this branch using `feat-rust`: https://github.com/smithy-lang/smithy-dafny/actions/runs/10460169241/job/28965787879 (only fixes the Rust tests, the other languages aren't set up to build Dafny from source)

TestModels/.gitignore

@@ -10,8 +10,7 @@
 **/runtimes/java/src/test/dafny-generated/
 
 # Dafny Generated Rust
-# (Rust code generation is incomplete so we're patching and checking in for now)
-#**/runtimes/rust
+**/runtimes/rust/src/implementation_from_dafny.rs
 # Cargo.lock files should only be committed for binaries, not libraries
 **/Cargo.lock