Stop inherited method's unrecoverble stub

Stubbing inherited method with `any_instance` sometimes cause
SystemStackError, below is reproduction example.

```ruby
class SuperClass
  def foo; end
end

class SubClass < SuperClass
end

describe SubClass do
  it "workds fine at firstt" do
    SuperClass.any_instance.stub(:foo)
    SubClass.any_instance.stub(:foo)
  end

  it "cause SystemStackError after removing stub" do
    SubClass.new.foo # => SystemStackError raised
  end
end
```
`restore_original_method` for SubClass restores SuperClass's stubbed method, so that `SubClass#foo` is broken.

This commit prevent this problem by raising error immediately when SubClass's `any_instance` stub is defined.