resolve: Remove exported imports from maybe_unused_trait_imports

(cherry picked from commit b4a1fc7)

Author: petrochenkov

compiler/rustc_resolve/src/check_unused.rs

@@ -105,6 +105,7 @@ impl<'a, 'ra, 'tcx> UnusedImportCheckVisitor<'a, 'ra, 'tcx> {
         let def_id = self.r.owner_def_id(id);
         if self.r.effective_visibilities.is_exported(def_id) {
             self.check_import_as_underscore(use_tree, id);
+            self.r.maybe_unused_trait_imports.swap_remove(&def_id);
             return;
         }
 

tests/ui/imports/unused-import-issue-157420.rs

@@ -5,7 +5,7 @@
 #![warn(unused_imports)]
 
 pub use inner::*;
-use crate::outer::*; //~ WARN unused import: `crate::outer`
+use crate::outer::*;
 
 mod outer {
     pub mod inner {