Drop metadata_encoding_version.

Author: cjgillot

src/lib.rs

@@ -14,6 +14,7 @@ extern crate rustc_fs_util;
 extern crate rustc_hir;
 extern crate rustc_incremental;
 extern crate rustc_index;
+extern crate rustc_metadata;
 extern crate rustc_session;
 extern crate rustc_span;
 extern crate rustc_target;

src/metadata.rs

@@ -10,7 +10,7 @@ pub(crate) fn write_metadata<O: WriteMetadata>(tcx: TyCtxt<'_>, object: &mut O)
     use std::io::Write;
 
     let metadata = tcx.encode_metadata();
-    let mut compressed = tcx.metadata_encoding_version();
+    let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
     FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();
 
     object.add_rustc_section(