[Bug #20302] Multiple refinements cannot be applied to the same module

In the following code, the iclass tree of refinements in cref should be <iclass of Kernel@M2> -> <iclass of Kernel@M1> -> Kernel.

However, the iclass tree was broken because of code for included modules of refinements in rb_using_refinement().
Refinement#include is now removed, so this commit removes such unnecessary code.

```ruby
module M1
  refine(Kernel) do
    def f1 = :f1
  end
end

module M2
  refine(Kernel) do
    def f2 = :f2
  end
end

class Foo
  using M1
  using M2

  def test
    p f2 #=> :f2

    p f1 # expected => :f1
         # actual => undefined local variable or method 'f1' for an instance of Foo
  end
end

Foo.new.test
```

1 files changed, 0 insertions, 6 deletions

diff --git a/eval.c b/eval.c
index a330b9c8bc..0d74de483a 100644
--- a/eval.c
+++ b/eval.c
@@ -1276,12 +1276,6 @@ rb_using_refinement(rb_cref_t *cref, VALUE klass, VALUE module)
 
     RCLASS_M_TBL(c) = RCLASS_M_TBL(module);
 
-    module = RCLASS_SUPER(module);
-    while (module && module != klass) {
-        c = RCLASS_SET_SUPER(c, rb_include_class_new(module, RCLASS_SUPER(c)));
-        RB_OBJ_WRITE(c, &RCLASS_REFINED_CLASS(c), klass);
-        module = RCLASS_SUPER(module);
-    }
     rb_hash_aset(CREF_REFINEMENTS(cref), klass, iclass);
 }