proto: Update generated Rust code

Update the  Rust code that is generated from the `.proto` files, since
we've updated the `rust-protobuf` library in the previous commit. This
update is merely a version bump.

Author: apyrgio

proto/metadata.rs

@@ -1,4 +1,4 @@
-// This file is generated by rust-protobuf 2.20.0. Do not edit
+// This file is generated by rust-protobuf 2.22.0. Do not edit
 // @generated
 
 // https://github.com/rust-lang/rust-clippy/issues/702
@@ -21,7 +21,7 @@
 
 /// Generated files are compatible only with the same version
 /// of protobuf runtime.
-// const _PROTOBUF_VERSION_CHECK: () = ::protobuf::VERSION_2_20_0;
+// const _PROTOBUF_VERSION_CHECK: () = ::protobuf::VERSION_2_22_0;
 
 #[derive(PartialEq,Clone,Default)]
 pub struct KeyDerivationMetadata {