FormHelper#issue_assignees_dropdown_options never has multiple assignees

Only EE supports multiple issue assignees, so this CE code should not contain
code to have multiple assignees. EE will override the multiple issue assignees
feature by overriding this method.

app/helpers/form_helper.rb

@@ -16,8 +16,8 @@ module FormHelper
     end
   end
 
-  def issue_dropdown_options(issuable, has_multiple_assignees = true)
-    options = {
+  def issue_assignees_dropdown_options
+    {
       toggle_class: 'js-user-search js-assignee-search js-multiselect js-save-user-data',
       title: 'Select assignee',
       filter: true,
@@ -27,8 +27,8 @@ module FormHelper
         first_user: current_user&.username,
         null_user: true,
         current_user: true,
-        project_id: issuable.project.try(:id),
-        field_name: "#{issuable.class.model_name.param_key}[assignee_ids][]",
+        project_id: @project.id,
+        field_name: 'issue[assignee_ids][]',
         default_label: 'Unassigned',
         'max-select': 1,
         'dropdown-header': 'Assignee',
@@ -38,13 +38,5 @@ module FormHelper
         current_user_info: current_user.to_json(only: [:id, :name])
       }
     }
-
-    if has_multiple_assignees
-      options[:title] = 'Select assignee(s)'
-      options[:data][:'dropdown-header'] = 'Assignee(s)'
-      options[:data].delete(:'max-select')
-    end
-
-    options
   end
 end

app/views/shared/issuable/form/_metadata_issue_assignee.html.haml

@@ -7,5 +7,5 @@
     - if issuable.assignees.length === 0
       = hidden_field_tag "#{issuable.to_ability_name}[assignee_ids][]", 0, id: nil, data: { meta: '' }
 
-    = dropdown_tag(users_dropdown_label(issuable.assignees), options: issue_dropdown_options(issuable,false))
+    = dropdown_tag(users_dropdown_label(issuable.assignees), options: issue_assignees_dropdown_options)
   = link_to 'Assign to me', '#', class: "assign-to-me-link #{'hide' if issuable.assignees.include?(current_user)}"

spec/features/issues/form_spec.rb

@@ -31,8 +31,8 @@ describe 'New/edit issue', :feature, :js do
         # the original method, resulting in infinite recurison when called.
         # This is likely a bug with helper modules included into dynamically generated view classes.
         # To work around this, we have to hold on to and call to the original implementation manually.
-        original_issue_dropdown_options = FormHelper.instance_method(:issue_dropdown_options)
-        allow_any_instance_of(FormHelper).to receive(:issue_dropdown_options).and_wrap_original do |original, *args|
+        original_issue_dropdown_options = FormHelper.instance_method(:issue_assignees_dropdown_options)
+        allow_any_instance_of(FormHelper).to receive(:issue_assignees_dropdown_options).and_wrap_original do |original, *args|
           options = original_issue_dropdown_options.bind(original.receiver).call(*args)
           options[:data][:per_page] = 2