Compute proc_macros in resolutions.

compiler/rustc_ast/src/ast.rs

@@ -502,13 +502,6 @@ pub struct Crate {
     pub attrs: Vec<Attribute>,
     pub items: Vec<P<Item>>,
     pub span: Span,
-    /// The order of items in the HIR is unrelated to the order of
-    /// items in the AST. However, we generate proc macro harnesses
-    /// based on the AST order, and later refer to these harnesses
-    /// from the HIR. This field keeps track of the order in which
-    /// we generated proc macros harnesses, so that we can map
-    /// HIR proc macros items back to their harness items.
-    pub proc_macros: Vec<NodeId>,
 }
 
 /// Possible values inside of compile-time attribute lists.