Remove `add_remove_ci_variable_spec.rb`
Per discussion in #1533 (closed), we have determined that add_remove_ci_variable_spec.rb
can now be recommended for feature specs. Removing this spec from E2E test bank.
Since this is a smoke test, I created a follow up issue to ensure feature tests are added to maintain adequate coverage gitlab-org/gitlab#391637 (closed)
Edited by Tiffany Rea