Remove ci_instance_level_variables feature flag

Removes the feature flag and updates documentation to reflect this

app/models/ci/instance_variable.rb

@@ -45,13 +45,5 @@ module Ci
         end
       end
     end
-
-    private
-
-    def validate_plan_limit_not_exceeded
-      if Gitlab::Ci::Features.instance_level_variables_limit_enabled?
-        super
-      end
-    end
   end
 end

app/models/concerns/ci/contextable.rb

@@ -84,8 +84,6 @@ module Ci
     end
 
     def secret_instance_variables
-      return [] unless ::Feature.enabled?(:ci_instance_level_variables, project, default_enabled: true)
-
       project.ci_instance_variables_for(ref: git_ref)
     end
 

doc/api/instance_level_ci_variables.md

 # Instance-level CI/CD variables API
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/14108) in GitLab 13.0
-> - It's deployed behind a feature flag, enabled by default.
-> - It's enabled on GitLab.com.
-> - It's recommended for production use.
-> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-instance-level-cicd-variables-core-only). **(CORE ONLY)**
+> - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/218249) in GitLab 13.2.
 
 ## List all instance variables
 
@@ -140,22 +137,3 @@ DELETE /admin/ci/variables/:key
 ```shell
 curl --request DELETE --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/admin/ci/variables/VARIABLE_1"
 ```
-
-### Enable or disable instance-level CI/CD variables **(CORE ONLY)**
-
-Instance-level CI/CD variables is under development but ready for production use.
-It is deployed behind a feature flag that is **enabled by default**.
-[GitLab administrators with access to the GitLab Rails console](../administration/feature_flags.md)
-can opt to disable it for your instance.
-
-To disable it:
-
-```ruby
-Feature.disable(:ci_instance_level_variables)
-```
-
-To enable it:
-
-```ruby
-Feature.enable(:ci_instance_level_variables)
-```

doc/ci/variables/README.md

@@ -458,9 +458,6 @@ The UI interface for Instance-level CI/CD variables is under development but rea
 It is deployed behind a feature flag that is **enabled by default**.
 [GitLab administrators with access to the GitLab Rails console](../../administration/feature_flags.md) can opt to disable it for your instance.
 
-NOTE: **Note:**
-This feature will not work if the [instance-level CI/CD variables API feature flag is disabled](../../api/instance_level_ci_variables.md#enable-or-disable-instance-level-cicd-variables-core-only).
-
 To disable it:
 
 ```ruby

lib/gitlab/ci/features.rb

@@ -18,10 +18,6 @@ module Gitlab
         ::Feature.enabled?(:ci_job_heartbeats_runner, project, default_enabled: true)
       end
 
-      def self.instance_level_variables_limit_enabled?
-        ::Feature.enabled?(:ci_instance_level_variables_limit, default_enabled: true)
-      end
-
       def self.pipeline_fixed_notifications?
         ::Feature.enabled?(:ci_pipeline_fixed_notifications, default_enabled: true)
       end

spec/models/ci/build_spec.rb

@@ -3301,17 +3301,6 @@ RSpec.describe Ci::Build do
         expect(build.scoped_variables_hash).not_to include('MY_VAR': 'my value 1')
       end
     end
-
-    context 'when CI instance variables are disabled' do
-      before do
-        create(:ci_instance_variable, key: 'MY_VAR', value: 'my value 1')
-        stub_feature_flags(ci_instance_level_variables: false)
-      end
-
-      it 'does not include instance level variables' do
-        expect(build.scoped_variables_hash).not_to include('MY_VAR': 'my value 1')
-      end
-    end
   end
 
   describe '#any_unmet_prerequisites?' do

spec/models/ci/instance_variable_spec.rb

@@ -15,21 +15,6 @@ RSpec.describe Ci::InstanceVariable do
     subject { build(:ci_instance_variable) }
   end
 
-  context 'with instance level variable feature flag disabled' do
-    let(:plan_limits) { create(:plan_limits, :default_plan) }
-
-    before do
-      stub_feature_flags(ci_instance_level_variables_limit: false)
-      plan_limits.update(described_class.limit_name => 1)
-      create(:ci_instance_variable)
-    end
-
-    it 'can create new models exceeding the plan limits', :aggregate_failures do
-      expect { subject.save }.to change { described_class.count }
-      expect(subject.errors[:base]).to be_empty
-    end
-  end
-
   describe '.unprotected' do
     subject { described_class.unprotected }