Drop metadata_encoding_version.
diff --git a/Cargo.lock b/Cargo.lock
index df7d844..1d3b539 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3677,6 +3677,7 @@
  "rustc_incremental",
  "rustc_index",
  "rustc_llvm",
+ "rustc_metadata",
  "rustc_middle",
  "rustc_serialize",
  "rustc_session",