Rename elements and method on page objects

And adjust the affected test accordingly.

The idea is to improve readability by having more descriptive
names.

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

@@ -13,7 +13,7 @@ module QA
             end
 
             view 'app/assets/javascripts/vue_shared/components/issue/related_issuable_item.vue' do
-              element :remove_issue_button
+              element :remove_related_issue_button
             end
 
             view 'ee/app/assets/javascripts/epic/components/epic_header.vue' do
@@ -49,7 +49,7 @@ module QA
             end
 
             def remove_issue_from_epic
-              click_element :remove_issue_button
+              click_element :remove_related_issue_button
             end
 
             def click_edit_button

qa/qa/page/project/issue/show.rb

@@ -36,7 +36,7 @@ module QA
           end
 
           view 'app/assets/javascripts/vue_shared/components/issue/related_issuable_item.vue' do
-            element :remove_issue_button
+            element :remove_related_issue_button
           end
 
           view 'app/helpers/dropdowns_helper.rb' do
@@ -80,8 +80,8 @@ module QA
             click_element(:milestone_link)
           end
 
-          def click_remove_issue_button
-            click_element(:remove_issue_button)
+          def click_remove_related_issue_button
+            click_element(:remove_related_issue_button)
           end
 
           # Adds a comment to an issue

qa/qa/specs/features/ee/browser_ui/2_plan/related_issues/related_issues_spec.rb

@@ -37,7 +37,7 @@ module QA
           expect(show).to have_content("marked this issue as related to ##{issue_2.iid}")
           expect(show.related_issuable_item).to have_content(issue_2.title)
 
-          show.click_remove_issue_button
+          show.click_remove_related_issue_button
 
           expect(show).to have_content("removed the relation with ##{issue_2.iid}")
           expect(show).not_to have_content(issue_2.title)