Delete mailer queue

because we never use sidekiq_mailer gem. The sidekiq queue to send mails names 'default',not 'mailer' .

2014-07-03T10:26:06Z 11190 TID-1wru8c Sidekiq::Extensions::DelayedMailer JID-635dd95ab68f2c6695da15b7 INFO: start
2014-07-03T10:26:06Z 11190 TID-1wru8c Sidekiq::Extensions::DelayedMailer JID-635dd95ab68f2c6695da15b7 INFO: fail: 0.265 sec
2014-07-03T10:26:06Z 11190 TID-1wru8c WARN: {"retry"=>true, "queue"=>"default", "class"=>"Sidekiq::Extensions::DelayedMailer", "args"=>["---\n- !ruby/class 'Notify'\n- :project_was_moved_email\n- - 1299\n  - 4\n"], "jid"=>"635dd95ab68f2c6695da15b7", "enqueued_at"=>1404381797.3215425, "error_message"=>"Connection reset by peer", "error_class"=>"Errno::ECONNRESET", "failed_at"=>"2014-07-03T10:03:20Z", "retry_count"=>6, "retried_at"=>2014-07-03 10:26:06 UTC}