Remove issue observer

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/observers/issue_observer.rb

-class IssueObserver < BaseObserver
-  def after_close(issue, transition)
-    notification.close_issue(issue, current_user)
-    event_service.close_issue(issue, current_user)
-    create_note(issue)
-    execute_hooks(issue)
-  end
-
-  def after_reopen(issue, transition)
-    event_service.reopen_issue(issue, current_user)
-    create_note(issue)
-    execute_hooks(issue)
-  end
-
-  protected
-
-  # Create issue note with service comment like 'Status changed to closed'
-  def create_note(issue)
-    Note.create_status_change_note(issue, issue.project, current_user, issue.state, current_commit)
-  end
-
-  def create_assignee_note(issue)
-    Note.create_assignee_change_note(issue, issue.project, current_user, issue.assignee)
-  end
-
-  def execute_hooks(issue)
-    issue.project.execute_hooks(issue.to_hook_data, :issue_hooks)
-  end
-end

config/application.rb

@@ -21,7 +21,6 @@ module Gitlab
     # Activate observers that should always be running.
     config.active_record.observers = :milestone_observer,
                                      :project_activity_cache_observer,
-                                     :issue_observer,
                                      :key_observer,
                                      :merge_request_observer,
                                      :note_observer,