message: Provide default MetadataLoader
diff: use rustc_codegen_ssa::CodegenResults;
  use rustc_errors::ErrorReported;
  use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
  -use rustc_middle::middle::cstore::{EncodedMetadata, MetadataLoader};
  +use rustc_middle::middle::cstore::EncodedMetadata;
  use rustc_session::config::OutputFilenames;
  use rustc_session::Session;
  @@ -163,10 +163,6 @@ fn init(&self, sess: &Session) {
  }
  }
  - fn metadata_loader(&self) -> Box<dyn MetadataLoader + Sync> {
  - Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
  - }
  -
  fn target_features(&self, _sess: &Session) -> Vec<rustc_span::Symbol> {
  vec![]
  }
  