Update Kernel#method_missing tests for new NoMethodError message.

Also removed tests that depends on implementation details of the default
`method_missing` behavior.

test/t/kernel.rb

@@ -366,48 +366,14 @@ assert('Kernel#method_missing', '15.3.1.3.30') do
   begin
     no_super_test.no_super_method_named_this
   rescue NoMethodError => e
-    assert_equal "undefined method 'no_super_method_named_this' for #{no_super_test}", e.message
+    assert_equal "undefined method 'no_super_method_named_this'", e.message
   end
 
   a = String.new
   begin
     a.no_method_named_this
   rescue NoMethodError => e
-    assert_equal "undefined method 'no_method_named_this' for \"\"", e.message
-  end
-
-  class ShortInspectClass
-    def inspect
-      'An inspect string'
-    end
-  end
-  b = ShortInspectClass.new
-  begin
-    b.no_method_named_this
-  rescue NoMethodError => e
-    assert_equal "undefined method 'no_method_named_this' for An inspect string", e.message
-  end
-
-  class LongInspectClass
-    def inspect
-      "A" * 70
-    end
-  end
-  c = LongInspectClass.new
-  begin
-    c.no_method_named_this
-  rescue NoMethodError => e
-    assert_equal "undefined method 'no_method_named_this' for #{c}", e.message
-  end
-
-  class NoInspectClass
-    undef inspect
-  end
-  d = NoInspectClass.new
-  begin
-    d.no_method_named_this
-  rescue NoMethodError => e
-    assert_equal "undefined method 'no_method_named_this' for #{d}", e.message
+    assert_equal "undefined method 'no_method_named_this'", e.message
   end
 end