[imaplib2 removal] Revert "Implementation of IMAP IDLE"

This reverts commit 3847d0ba9d.

offlineimap.conf

@@ -307,19 +307,6 @@ remoteuser = username
 #
 # reference = Mail
 
-# In between synchronisations, OfflineIMAP can monitor mailboxes for new
-# messages using the IDLE command. If you want to enable this, specify here
-# the folders you wish to monitor. Note that the IMAP protocol requires a
-# separate connection for each folder monitored in this way, so setting
-# this option will force settings for:
-#     maxconnections - to be at least the number of folders you give
-#     holdconnectionopen - to be true
-#     keepalive - to be 29 minutes unless you specify otherwise
-# This option should return a Python list. For example
-#
-# idlefolders = ['INBOX', 'INBOX.Alerts']
-#
-
 # OfflineIMAP can use multiple connections to the server in order
 # to perform multiple synchronization actions simultaneously.
 # This may place a higher burden on the server.  In most cases,