Do not set default values for deprecated fdw settings

Signed-off-by: Balasankar "Balu" C <balasankarc@autistici.org>

changelogs/unreleased/fix-fdw-deprecation-notice.yml

+---
+title: Fix geo fdw deprecation message
+merge_request: 4528
+author:
+type: fixed

files/gitlab-cookbooks/gitlab-ee/libraries/geo_postgresql.rb

 module GeoPostgresql
   class << self
     def parse_variables
-      Gitlab['geo_postgresql']['fdw_external_user'] ||=
-        Gitlab['gitlab_rails']['db_username'] || node['gitlab']['gitlab-rails']['db_username']
-
-      Gitlab['geo_postgresql']['fdw_external_password'] ||=
-        Gitlab['gitlab_rails']['db_password'] || node['gitlab']['gitlab-rails']['db_password']
-
       postgresql_dir = Gitlab['geo_postgresql']['dir'] || node['gitlab']['geo-postgresql']['dir']
       Gitlab['geo_postgresql']['unix_socket_directory'] ||= postgresql_dir