Unset the assignee field using the x marker

We no longer have an empty option in the user autocompleter,
but a clear button

spec/features/work_packages/edit_work_package_spec.rb

@@ -168,7 +168,9 @@ describe 'edit work package',
     wp_page.expect_attributes assignee: manager.name
     wp_page.expect_activity_message("Assignee set to #{manager.name}")
 
-    wp_page.update_attributes assignee: '-'
+    field = wp_page.edit_field :assignee
+    field.unset_value
+
     wp_page.expect_attributes assignee: '-'
 
     wp_page.visit!

spec/support/components/autocompleter/ng_select_autocomplete_helpers.rb

@@ -56,6 +56,12 @@ module Components::Autocompleter
       from_element.find('.ng-input input')
     end
 
+    ##
+    # clear the ng select field
+    def ng_select_clear(from_element)
+      from_element.find('.ng-clear-wrapper', visible: :all).click
+    end
+
     def select_autocomplete(element, query:, select_text: nil, results_selector: nil, wait_dropdown_open: true)
       target_dropdown = search_autocomplete(element,
                                             query:,

spec/support/edit_fields/edit_field.rb

@@ -164,14 +164,15 @@ class EditField
   ##
   # Set or select the given value.
   # For fields of type select, will check for an option with that value.
-  def unset_value(content, multi = false)
+  def unset_value(content = nil, multi = false)
+    activate!
     scroll_to_element(input_element)
 
     if field_type.end_with?('-autocompleter')
       if multi
         page.find('.ng-value-label', visible: :all, text: content).sibling('.ng-value-icon').click
       else
-        page.find('.ng-dropdown-panel .ng-option', visible: :all, text: '-').click
+        ng_select_clear(field_container)
       end
     else
       input_element.set('')