Remove remove_import_data_on_failure feature flag

Changelog: removed

app/models/project_import_state.rb

@@ -58,10 +58,8 @@ class ProjectImportState < ApplicationRecord
     end
 
     after_transition any => :failed do |state, _|
-      if Feature.enabled?(:remove_import_data_on_failure, state.project, default_enabled: :yaml)
       state.project.remove_import_data
     end
-    end
 
     after_transition started: :finished do |state, _|
       project = state.project

config/feature_flags/development/remove_import_data_on_failure.yml

----
-name: remove_import_data_on_failure
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/80074
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/352156
-milestone: '14.8'
-type: development
-group: group::source code
-default_enabled: true

spec/models/project_import_state_spec.rb

@@ -89,19 +89,6 @@ RSpec.describe ProjectImportState, type: :model do
         import_state.mark_as_failed(error_message)
       end.to change { project.reload.import_data }.from(import_data).to(nil)
     end
-
-    context 'when remove_import_data_on_failure feature flag is disabled' do
-      it 'removes project import data' do
-        stub_feature_flags(remove_import_data_on_failure: false)
-
-        project = create(:project, import_data: ProjectImportData.new(data: { 'test' => 'some data' }))
-        import_state = create(:import_state, :started, project: project)
-
-        expect do
-          import_state.mark_as_failed(error_message)
-        end.not_to change { project.reload.import_data }
-      end
-    end
   end
 
   describe '#human_status_name' do