Add Boards::DestroyService service to remove boards

app/services/boards/destroy_service.rb

+module Boards
+  class DestroyService < Boards::BaseService
+    def execute(board)
+      board.destroy
+    end
+  end
+end

spec/services/boards/destroy_service_spec.rb

+require 'spec_helper'
+
+describe Boards::DestroyService, services: true do
+  describe '#execute' do
+    it 'removes board from project' do
+      project = create(:empty_project)
+      board   = create(:board, project: project)
+
+      service = described_class.new(project, double)
+
+      expect { service.execute(board) }.to change(project.boards, :count).by(-1)
+    end
+  end
+end