Revert 219658 - Update routes for lost-and-found group and projects

What does this MR do?

Reverts !33653 (merged) since it is causing a PG::UniqueViolation error when run on production:

PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_routes_on_path"
     DETAIL:  Key (path)=(lost-and-found) already exists.

Reverting this should be safe and will not require any updates on production.

Full stack trace of the issue:

     == 20200602143020 UpdateRoutesForLostAndFoundGroupAndOrphanedProjects: migrating
     rake aborted!
     StandardError: An error has occurred, this and all later migrations canceled:
     PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_routes_on_path"
     DETAIL:  Key (path)=(lost-and-found) already exists.
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:78:in `ensure_route!'
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:153:in `up'
     /opt/gitlab/embedded/bin/bundle:23:in `load'
     /opt/gitlab/embedded/bin/bundle:23:in `<main>'
     Caused by:
     ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_routes_on_path"
     DETAIL:  Key (path)=(lost-and-found) already exists.
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:78:in `ensure_route!'
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:153:in `up'
     /opt/gitlab/embedded/bin/bundle:23:in `load'
     /opt/gitlab/embedded/bin/bundle:23:in `<main>'
     Caused by:
     PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_routes_on_path"
     DETAIL:  Key (path)=(lost-and-found) already exists.
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:78:in `ensure_route!'
     /opt/gitlab/embedded/service/gitlab-rails/db/post_migrate/20200602143020_update_routes_for_lost_and_found_group_and_orphaned_projects.rb:153:in `up'
     /opt/gitlab/embedded/bin/bundle:23:in `load'
     /opt/gitlab/embedded/bin/bundle:23:in `<main>'
     Tasks: TOP => db:migrate
     (See full trace by running task with --trace)?;

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