Remove Project#clusters export

lib/gitlab/import_export/import_export.yml

@@ -54,8 +54,6 @@ project_tree:
   - :auto_devops
   - :triggers
   - :pipeline_schedules
-  - clusters:
-    - :application_helm
   - :services
   - :hooks
   - protected_branches:

lib/gitlab/import_export/relation_factory.rb

@@ -8,8 +8,6 @@ module Gitlab
                     triggers: 'Ci::Trigger',
                     pipeline_schedules: 'Ci::PipelineSchedule',
                     builds: 'Ci::Build',
-                    clusters: 'Clusters::Cluster',
-                    application_helm: 'Clusters::Applications::Helm',
                     hooks: 'ProjectHook',
                     merge_access_levels: 'ProtectedBranch::MergeAccessLevel',
                     push_access_levels: 'ProtectedBranch::PushAccessLevel',

spec/lib/gitlab/import_export/all_models.yml

@@ -147,22 +147,6 @@ deploy_keys:
 - user
 - deploy_keys_projects
 - projects
-clusters:
-- application_helm
-- cluster_projects
-- projects
-- user
-- provider_gcp
-- platform_kubernetes
-cluster_projects:
-- projects
-- clusters
-provider_gcp:
-- cluster
-platform_kubernetes:
-- cluster
-application_helm:
-- cluster
 services:
 - project
 - service_hook