Prune epics management end-to-end test

This test fails intermittently on CI in the assertion after editing
the epic title, as it can be seen in the below job:

https://gitlab.com/gitlab-org/gitlab-qa/-/jobs/387863693

Editing and deletion of epics have already a good coverage in lower
level tests, as it can be seen from the following files:

- ee/spec/features/epics/update_epic_spec.rb
- ee/spec/features/epics/delete_epic_spec.rb

With that, it's safe to remove these steps from the end-to-end test
suite and still be sure that these functionalities are still being
tested.

Besides that, now the test is focused on only one thing.

Finally, this change reduces the code in 17 lines.

qa/qa/specs/features/ee/browser_ui/2_plan/epic/epics_management_spec.rb

@@ -7,30 +7,13 @@ module QA
         Flow::Login.sign_in
       end
 
-      it 'creates, edits, and deletes an epic' do
+      it 'creates an epic' do
         epic_title = 'Epic created via GUI'
-        epic = EE::Resource::Epic.fabricate_via_browser_ui! do |epic|
+        EE::Resource::Epic.fabricate_via_browser_ui! do |epic|
           epic.title = epic_title
         end
 
         expect(page).to have_content(epic_title)
-
-        epic_edited_title = 'Epic edited via GUI'
-        EE::Page::Group::Epic::Show.perform(&:click_edit_button)
-        EE::Page::Group::Epic::Edit.perform do |edit|
-          edit.set_title(epic_edited_title)
-          edit.save_changes
-
-          expect(edit).to have_content(epic_edited_title)
-        end
-
-        epic.visit!
-        EE::Page::Group::Epic::Show.perform(&:click_edit_button)
-        EE::Page::Group::Epic::Edit.perform(&:delete_epic)
-
-        EE::Page::Group::Epic::Index.perform do |index|
-          expect(index).to have_no_epic(epic_edited_title)
-        end
       end
 
       context 'Resources created via API' do