De-quarantine e2e test for issue suggestions

According to https://bit.ly/2JTPCcF

Now that https://gitlab.com/gitlab-org/gitlab-ce/issues/60355
is closed we can de-quarantine this test.

qa/qa/specs/features/browser_ui/2_plan/issue/issue_suggestions_spec.rb

 # frozen_string_literal: true
 
 module QA
-  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/53
-  context 'Plan', :quarantine do
+  context 'Plan' do
     describe 'issue suggestions' do
       let(:issue_title) { 'Issue Lists are awesome' }