Remove box syntax from Box<function pointer> construction

The function pointer should be extremely small, close to pointer size.

src/librustdoc/core.rs

@@ -285,7 +285,7 @@ pub(crate) fn create_config(
         diagnostic_output: DiagnosticOutput::Default,
         lint_caps,
         parse_sess_created: None,
-        register_lints: Some(box crate::lint::register_lints),
+        register_lints: Some(Box::new(crate::lint::register_lints)),
         override_queries: Some(|_sess, providers, _external_providers| {
             // Most lints will require typechecking, so just don't run them.
             providers.lint_mod = |_, _| {};