Remove RawDefId tracking infrastructure from incr. comp. framework.

This infrastructure is obsolete now with the new encoding scheme for
the DefPathHash->DefIndex maps in crate metadata.

compiler/rustc_query_system/src/dep_graph/dep_node.rs

@@ -53,18 +53,6 @@ use std::hash::Hash;
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Encodable, Decodable)]
 pub struct DepNode<K> {
     pub kind: K,
-    // Important - whenever a `DepNode` is constructed, we need to make
-    // sure to register a `DefPathHash -> DefId` mapping if needed.
-    // This is currently done in two places:
-    //
-    // * When a `DepNode::construct` is called, `arg.to_fingerprint()`
-    //   is responsible for calling `OnDiskCache::store_foreign_def_id_hash`
-    //   if needed
-    // * When we serialize the on-disk cache, `OnDiskCache::serialize` is
-    //   responsible for calling `DepGraph::register_reused_dep_nodes`.
-    //
-    // FIXME: Enforce this by preventing manual construction of `DefNode`
-    // (e.g. add a `_priv: ()` field)
     pub hash: PackedFingerprint,
 }