Remove non-ASCII comments

This fixes the build when trying to generate the rdoc.

Index: class.c
--- class.c.orig
+++ class.c
@@ -705,9 +705,9 @@ static VALUE
 class_associate_super(VALUE klass, VALUE super, bool init)
 {
     if (super && !UNDEF_P(super)) {
-        // Only maintain subclass lists for T_CLASS→T_CLASS relationships.
+        // Only maintain subclass lists for T_CLASS->T_CLASS relationships.
         // Include/prepend inserts ICLASSes into the super chain, but T_CLASS
-        // subclass lists should track only the immutable T_CLASS→T_CLASS link.
+        // subclass lists should track only the immutable T_CLASS->T_CLASS link.
         if (RB_TYPE_P(klass, T_CLASS) && RB_TYPE_P(super, T_CLASS)) {
             class_switch_superclass(super, klass);
         }
