Revert "Enqueue "select2" was missing in "background" field."

This reverts commit 5ef4c8b27369058f91f20d148b56efe37cae5f59.
Enqueue "field-select-js" was missing in "background" field.
Merge pull request #758 from meydjer/master

Enqueue "field-select-js" was missing in "background" field.