Fix broken qa test

With the feature flag `:epic_new_issue` enabled by default, the QA
test that adds/removes issue to/from epic was broken.

This commit fixes it by:

- Adjusting the page object views and a method
- Adding a new `data-qa-selector` attribute in an element
- Deleting a `data-qa-selector` attribute that is not in use any-
more.

ee/app/assets/javascripts/related_issues/constants.js

@@ -79,7 +79,6 @@ export const issuableIconMap = {
  * them inside i18n functions.
  */
 export const issuableQaClassMap = {
-  [issuableTypesMap.ISSUE]: 'qa-add-issues-button',
   [issuableTypesMap.EPIC]: 'qa-add-epics-button',
 };
 

ee/app/assets/javascripts/related_items_tree/components/issue_actions_split_button.vue

@@ -34,6 +34,7 @@ export default {
   <split-button
     :action-items="$options.actionItems"
     class="js-issue-actions-split-button"
+    data-qa-selector="issue_actions_split_button"
     menu-class="dropdown-menu-large"
     right
     size="sm"

qa/qa/ee/page/group/epic/show.rb

@@ -20,6 +20,10 @@ module QA
               element :add_issue_input
             end
 
+            view 'ee/app/assets/javascripts/related_items_tree/components/issue_actions_split_button.vue' do
+              element :issue_actions_split_button
+            end
+
             view 'ee/app/assets/javascripts/related_items_tree/components/tree_item.vue' do
               element :related_issue_item
             end
@@ -28,12 +32,8 @@ module QA
               element :remove_issue_button
             end
 
-            view 'ee/app/assets/javascripts/related_issues/constants.js' do
-              element :add_issues_button
-            end
-
             def add_issue_to_epic(issue_url)
-              click_element :add_issues_button
+              find_element(:issue_actions_split_button).find_all('button').first.click
               fill_element :add_issue_input, issue_url
               click_body
               click_element :add_issue_button