Remove duplicate code

This was added in !4860, but somehow the code was was already present in
9c000451, causing https://gitlab.com/gitlab-org/gitlab-ee/-/jobs/56081024
to fail.

lib/gitlab/utils.rb

@@ -68,14 +68,6 @@ module Gitlab
       nil
     end
 
-    # Used in EE
-    # Accepts either an Array or a String and returns an array
-    def ensure_array_from_string(string_or_array)
-      return string_or_array if string_or_array.is_a?(Array)
-
-      string_or_array.split(',').map(&:strip)
-    end
-
     # EE below
     def try_megabytes_to_bytes(size)
       Integer(size).megabytes