kernel.c, binding.c: use `MRB_SYM()` instead of `mrb_intern_lit()`.

mrbgems/mruby-binding/test/binding.c

 #include <mruby.h>
+#include <mruby/presym.h>
 
 static mrb_value
 binding_in_c(mrb_state *mrb, mrb_value self)
 {
-  return mrb_funcall_argv(mrb, mrb_obj_value(mrb->object_class), mrb_intern_lit(mrb, "binding"), 0, NULL);
+  return mrb_funcall_argv(mrb, mrb_obj_value(mrb->object_class), MRB_SYM(binding), 0, NULL);
 }
 
 void

src/kernel.c

@@ -589,7 +589,7 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
   else if (mrb_nil_p(self)) {
     return mrb_false_value();
   }
-  else if (!mrb_respond_to(mrb, self, mrb_intern_lit(mrb, "to_a"))) {
+  else if (!mrb_respond_to(mrb, self, MRB_SYM(to_a))) {
     mrb_value c = mrb_funcall_argv(mrb, self, eqq, 1, &v);
     if (mrb_test(c)) return mrb_true_value();
     return mrb_false_value();