Make AutoMoveOneLineHandler::Run explicitly ignore caret position when the destination is removed

The test case removes entire the <output> during deleting its content and that occurs during it moves the content in <div> into the preceding <ruby>. Therefore, the destination becomes not connected to the document so that it fails to track the range of moved contents in the document.

Then, the code does not explicitly mark the caret position is not necessary. So, we just need to do it.

Differential Revision: https://phabricator.services.mozilla.com/D198148

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1872428 gecko-commit: fb88413de9c123d2c96fc69bdb3545586a7b0015 gecko-reviewers: m_kato