Remove ci_file_based_cache feature flag

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

@@ -51,8 +51,6 @@ module Gitlab
             end
 
             def hash_of_the_latest_changes
-              return unless Feature.enabled?(:ci_file_based_cache, @pipeline.project, default_enabled: true)
-
               ids = files.map { |path| last_commit_id_for_path(path) }
               ids = ids.compact.sort.uniq
 

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

@@ -83,16 +83,6 @@ describe Gitlab::Ci::Pipeline::Seed::Build::Cache do
         it_behaves_like 'version and gemfile files'
       end
 
-      context 'with feature flag disabled' do
-        let(:files) { ['VERSION', 'Gemfile.zip'] }
-
-        before do
-          stub_feature_flags(ci_file_based_cache: false)
-        end
-
-        it_behaves_like 'default key'
-      end
-
       context 'with files ending with /' do
         let(:files) { ['Gemfile.zip/'] }