WidgetOnDemand: Turn off form and entity validation for ajax calls or at least make this possible

Problem/Motivation

#2673984: Turn off form and entity validation for ajax calls or at least make this possible is trying to turn off form and entity validation for ajax calls or at least make this possible. If this happens we have to this change here as well.

Proposed resolution

Set #validate to an empty array for our ajax submit, so that we do not trigger the form and entity validation.

Remaining tasks

It depends on what will happen with #2673984: Turn off form and entity validation for ajax calls or at least make this possible.

User interface changes

none.

API changes

none.

Data model changes

none.