rustc_ast: Do not panic by default when visiting macro calls

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -344,10 +344,6 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
         visit::walk_item(self, item);
         self.in_root = prev_in_root;
     }
-
-    fn visit_mac(&mut self, mac: &'a ast::MacCall) {
-        visit::walk_mac(self, mac)
-    }
 }
 
 // Creates a new module which looks like:

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -130,10 +130,6 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
         }
         smallvec![P(item)]
     }
-
-    fn visit_mac(&mut self, _mac: &mut ast::MacCall) {
-        // Do nothing.
-    }
 }
 
 // Beware, this is duplicated in librustc_passes/entry.rs (with
@@ -201,10 +197,6 @@ impl<'a> MutVisitor for EntryPointCleaner<'a> {
 
         smallvec![item]
     }
-
-    fn visit_mac(&mut self, _mac: &mut ast::MacCall) {
-        // Do nothing.
-    }
 }
 
 /// Crawl over the crate, inserting test reexports and the test main function