Refactor out empty constant

PROJECT_ONLY_APPLICATIONS is now empty so refactor that out and any code
that uses it.

app/models/clusters/cluster.rb

@@ -9,8 +9,6 @@ module Clusters
 
     self.table_name = 'clusters'
 
-    PROJECT_ONLY_APPLICATIONS = {
-    }.freeze
     APPLICATIONS = {
       Applications::Helm.application_name => Applications::Helm,
       Applications::Ingress.application_name => Applications::Ingress,
@@ -20,7 +18,7 @@ module Clusters
       Applications::Jupyter.application_name => Applications::Jupyter,
       Applications::Knative.application_name => Applications::Knative,
       Applications::ElasticStack.application_name => Applications::ElasticStack
-    }.merge(PROJECT_ONLY_APPLICATIONS).freeze
+    }.freeze
     DEFAULT_ENVIRONMENT = '*'
     KUBE_INGRESS_BASE_DOMAIN = 'KUBE_INGRESS_BASE_DOMAIN'
 

app/services/clusters/applications/base_service.rb

@@ -64,19 +64,13 @@ module Clusters
       end
 
       def invalid_application?
-        unknown_application? || (!cluster.project_type? && project_only_application?) || (application_name == Applications::ElasticStack.application_name && !Feature.enabled?(:enable_cluster_application_elastic_stack))
+        unknown_application? || (application_name == Applications::ElasticStack.application_name && !Feature.enabled?(:enable_cluster_application_elastic_stack))
       end
 
       def unknown_application?
         Clusters::Cluster::APPLICATIONS.keys.exclude?(application_name)
       end
 
-      # These applications will need extra configuration to enable them to work
-      # with groups of projects
-      def project_only_application?
-        Clusters::Cluster::PROJECT_ONLY_APPLICATIONS.include?(application_name)
-      end
-
       def application_name
         params[:application]
       end