Should not unset 'title' key in element array

Problem/Motivation

Came across this issue when trying to save a media item with no value in the remote url field. The Core Link module is expcting the "title" key be present in the element array and throws an error because its not.

Warning: Trying to access array offset on value of type null in Drupal\link\Plugin\Field\FieldWidget\LinkWidget::validateTitleNoLink() (line 176 of core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php).

Steps to reproduce

Go to add a new media item and try to save with an empty remote url value.

Proposed resolution

Patch attached