Suppress some warnings

```
.../ruby/test/ruby/test_keyword.rb:3509: warning: assigned but unused variable - bug8993
.../ruby/test/ruby/test_object.rb:83: warning: assigned but unused variable - f
.../ruby/test/ruby/test_object.rb:95: warning: method redefined; discarding old initialize_clone
.../ruby/test/ruby/test_object.rb:84: warning: previous definition of initialize_clone was here
```

test/ruby/test_keyword.rb

@@ -3506,7 +3506,6 @@ class TestKeywordArguments < Test::Unit::TestCase
   end
 
   def test_precedence_of_keyword_arguments_with_post_argument
-    bug8993 = '[ruby-core:57706] [Bug #8993]'
     a = Class.new do
       def foo(a, b, c=1, *d, e, f:2, **g)
         [a, b, c, d, e, f, g]

test/ruby/test_object.rb

@@ -80,7 +80,6 @@ class TestObject < Test::Unit::TestCase
       attr_reader :f
     end
     o = c.new
-    f = true
     def o.initialize_clone(_, freeze: true)
       @f = freeze
       super
@@ -92,6 +91,9 @@ class TestObject < Test::Unit::TestCase
     assert_kind_of c, clone
     assert_equal false, clone.f
 
+    class << o
+      remove_method(:initialize_clone)
+    end
     def o.initialize_clone(_)
       super
     end