Remove FF ci_rules_variables

It was already enabled by default

config/feature_flags/development/ci_rules_variables.yml

----
-name: ci_rules_variables
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/48752
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/289803
-milestone: '13.7'
-type: development
-group: group::pipeline authoring
-default_enabled: true

doc/ci/yaml/README.md

@@ -1436,14 +1436,7 @@ In this example, if the first rule matches, then the job has `when: manual` and
 #### `rules:variables`
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/209864) in GitLab 13.7.
-> - It was [deployed behind a feature flag](../../user/feature_flags.md), disabled by default.
-> - [Became enabled by default](https://gitlab.com/gitlab-org/gitlab/-/issues/289803) on GitLab 13.8.
-> - 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-rulesvariables). **(FREE SELF)**
-
-WARNING:
-This feature might not be available to you. Check the **version history** note above for details.
+> - [Feature flag removed](https://gitlab.com/gitlab-org/gitlab/-/issues/289803) in GitLab 13.10.
 
 You can use [`variables`](#variables) in `rules:` to define variables for specific conditions.
 
@@ -1465,25 +1458,6 @@ job:
     - echo "Run another script if $IS_A_FEATURE exists"
 ```
 
-##### Enable or disable rules:variables **(FREE SELF)**
-
-rules: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.
-
-To enable it:
-
-```ruby
-Feature.enable(:ci_rules_variables)
-```
-
-To disable it:
-
-```ruby
-Feature.disable(:ci_rules_variables)
-```
-
 #### Complex rule clauses
 
 To conjoin `if`, `changes`, and `exists` clauses with an `AND`, use them in the

lib/gitlab/ci/features.rb

@@ -59,10 +59,6 @@ module Gitlab
         ::Feature.enabled?(:ci_pipeline_editor_page, project, default_enabled: :yaml)
       end
 
-      def self.rules_variables_enabled?(project)
-        ::Feature.enabled?(:ci_rules_variables, project, default_enabled: true)
-      end
-
       def self.validate_build_dependencies?(project)
         ::Feature.enabled?(:ci_validate_build_dependencies, project, default_enabled: :yaml) &&
           ::Feature.disabled?(:ci_validate_build_dependencies_override, project)

lib/gitlab/ci/pipeline/seed/build.rb

@@ -169,15 +169,11 @@ module Gitlab
             strong_memoize(:rules_attributes) do
               next {} unless @using_rules
 
-              if ::Gitlab::Ci::Features.rules_variables_enabled?(@pipeline.project)
-                rules_variables_result = ::Gitlab::Ci::Variables::Helpers.merge_variables(
-                  @seed_attributes[:yaml_variables], rules_result.variables
-                )
+              rules_variables_result = ::Gitlab::Ci::Variables::Helpers.merge_variables(
+                @seed_attributes[:yaml_variables], rules_result.variables
+              )
 
-                rules_result.build_attributes.merge(yaml_variables: rules_variables_result)
-              else
-                rules_result.build_attributes
-              end
+              rules_result.build_attributes.merge(yaml_variables: rules_variables_result)
             end
           end
 

spec/lib/gitlab/ci/pipeline/seed/build_spec.rb

@@ -85,17 +85,6 @@ RSpec.describe Gitlab::Ci::Pipeline::Seed::Build do
                                                 { key: 'VAR2', value: 'var 2', public: true },
                                                 { key: 'VAR3', value: 'var 3', public: true }])
       end
-
-      context 'when FF ci_rules_variables is disabled' do
-        before do
-          stub_feature_flags(ci_rules_variables: false)
-        end
-
-        it do
-          is_expected.to include(yaml_variables: [{ key: 'VAR1', value: 'var 1', public: true },
-                                                  { key: 'VAR2', value: 'var 2', public: true }])
-        end
-      end
     end
 
     context 'with cache:key' do

spec/services/ci/create_pipeline_service/rules_spec.rb

@@ -180,20 +180,6 @@ RSpec.describe Ci::CreatePipelineService do
             expect(variables['VAR2']).to eq('my var 2')
             expect(variables['VAR3']).to be_nil
           end
-
-          context 'when FF ci_rules_variables is disabled' do
-            before do
-              stub_feature_flags(ci_rules_variables: false)
-            end
-
-            it 'does not affect variables' do
-              variables = job.scoped_variables_hash
-
-              expect(variables['VAR1']).to eq('my var 1')
-              expect(variables['VAR2']).to eq('my var 2')
-              expect(variables['VAR3']).to be_nil
-            end
-          end
         end
 
         context 'when matching to the second rule' do