Remove #ready? method in favor of #available?

Given https://github.com/helm/helm/issues/3338, I think that we should
exclude applications that are :update_errored, :updating as well.

app/models/clusters/concerns/application_status.rb

@@ -80,10 +80,6 @@ module Clusters
         installed? || updated?
       end
-      def ready?
-        installed? || updating? || updated? || update_errored?
-      end
-
       def update_in_progress?
         updating?
       end

app/services/prometheus/adapter_service.rb

@@ -30,7 +30,7 @@ module Prometheus
       return unless deployment_platform.respond_to?(:cluster)
       cluster = deployment_platform.cluster
-      return unless cluster.application_prometheus&.ready?
+      return unless cluster.application_prometheus&.available?
       cluster.application_prometheus
     end

spec/services/prometheus/adapter_service_spec.rb

@@ -22,7 +22,7 @@ describe Prometheus::AdapterService do
     context "prometheus service can't execute queries" do
       let(:prometheus_service) { double(:prometheus_service, can_query?: false) }
-      context 'with cluster with prometheus not yet installed' do
+      context 'with cluster with prometheus not available' do
         let!(:prometheus) { create(:clusters_applications_prometheus, :installable, cluster: cluster) }
         it 'returns nil' do
@@ -30,7 +30,7 @@ describe Prometheus::AdapterService do
         end
       end
-      context 'with cluster with prometheus installed' do
+      context 'with cluster with prometheus available' do
         let!(:prometheus) { create(:clusters_applications_prometheus, :installed, cluster: cluster) }
         it 'returns application handling all environments' do

spec/support/shared_examples/models/cluster_application_status_shared_examples.rb

@@ -138,32 +138,6 @@ shared_examples 'cluster application status specs' do |application_name|
     end
   end
-  describe '#ready?' do
-    using RSpec::Parameterized::TableSyntax
-
-    where(:trait, :ready) do
-      :not_installable  | false
-      :installable      | false
-      :scheduled        | false
-      :installing       | false
-      :installed        | true
-      :updating         | true
-      :updated          | true
-      :errored          | false
-      :update_errored   | true
-    end
-
-    with_them do
-      subject { build(application_name, trait) }
-
-      if params[:ready]
-        it { is_expected.to be_ready }
-      else
-        it { is_expected.not_to be_ready }
-      end
-    end
-  end
-
   describe '#available?' do
     using RSpec::Parameterized::TableSyntax