Remove `is_` prefix from predicate method names

gitlab-ce master % g grep -E 'def is_.+\?'
app/models/ci/runner.rb:145:    def is_runner_queue_value_latest?(value)
app/models/concerns/editable.rb:4:  def is_edited?
app/models/concerns/milestoneish.rb:73:  def is_group_milestone?
app/models/concerns/milestoneish.rb:77:  def is_project_milestone?
app/models/concerns/milestoneish.rb:81:  def is_legacy_group_milestone?
app/models/concerns/milestoneish.rb:85:  def is_dashboard_milestone?
app/models/dashboard_milestone.rb:6:  def is_dashboard_milestone?
app/models/group_milestone.rb:20:  def is_legacy_group_milestone?
app/models/milestone.rb:204:  def is_group_milestone?
app/models/milestone.rb:208:  def is_project_milestone?
app/models/network/graph.rb:162:    def is_overlap?(range, overlap_space)
app/models/project_services/chat_notification_service.rb:139:  def is_update?(data)
app/models/project_services/hipchat_service.rb:285:  def is_update?(data)
app/models/repository.rb:939:  def is_ancestor?(ancestor_id, descendant_id)
app/policies/project_policy.rb:296:  def is_team_member?
app/services/akismet_service.rb:10:  def is_spam?
app/services/git_push_service.rb:194:  def is_default_branch?
lib/gitlab/git/repository.rb:357:      def is_ancestor?(from, to)
lib/gitlab/health_checks/db_check.rb:13:        def is_successful?(result)
lib/gitlab/health_checks/redis/cache_check.rb:18:          def is_successful?(result)
lib/gitlab/health_checks/redis/queues_check.rb:18:          def is_successful?(result)
lib/gitlab/health_checks/redis/redis_check.rb:14:          def is_successful?(result)
lib/gitlab/health_checks/redis/shared_state_check.rb:18:          def is_successful?(result)
lib/gitlab/health_checks/simple_abstract_check.rb:33:      def is_successful?(result)
lib/system_check/base_check.rb:76:    def is_multi_check?
lib/tasks/gitlab/task_helpers.rb:105:    def is_gitlab_user?

For example, is_group_milestone? can just be group_milestone?, is_spam? can just be spam?, etc.