Cannot remove paragraph when using IEF Simple widget

Problem/Motivation

When a paragraph field is using the "Inline Entity Form - Simple" widget, you can remove paragraphs except for the last remaining one. This can prevent from saving the node form if the paragraph contains a required field.

Steps to reproduce

• Install latest Paragraphs and Inline Entity Form modules
• Create a new paragraph type "test" containing a required textfield
• Add a new Paragraphs field on the Basic page content type, with unlimited values and allowing the "test" paragraph type
• On the Manage form display tab, change the paragraphs field widget type to "Inline Entity Form - Simple"
• Create a new Basic page, fill the page title
• Try to remove the default paragraph
• Try to save the node without filling the paragraph required field

Proposed resolution

Allow removing all paragraphs when using the "Inline Entity Form - Simple" widget (it works when using other widgets)

Remaining tasks

User interface changes

API changes

Data model changes