feat(build): Decouple codgen from prost (#170)

interop/Cargo.toml

@@ -34,4 +34,4 @@ tracing-subscriber = "0.2.0-alpha"
 tracing-log = "0.1.0"
 
 [build-dependencies]
-tonic-build = { path = "../tonic-build" }
+tonic-build = { path = "../tonic-build", features=["prost"] }

interop/build.rs

@@ -1,7 +1,7 @@
 fn main() {
     let proto = "proto/grpc/testing/test.proto";
 
-    tonic_build::compile_protos(proto).unwrap();
+    tonic_build::prost::compile_protos(proto).unwrap();
 
     // prevent needing to rebuild if files (or deps) haven't changed
     println!("cargo:rerun-if-changed={}", proto);