Do not log civicrm_mailing_recipients table

Just as civicrm_mailing_event_* tables were excluded from logging in CRM-12300, I think it would make sense also to exclude civicrm_mailing_recipients. This gets cleared & repopulated in CRM_Mailing_BAO_Mailing::getRecipients().

I saw an example recently where a mailing with 73k recipients had 1.2 million entries in log_civicrm_mailing_recipients, just for that mailing (92 million in total in that table). That's an awful lot of inserts and MySQL was struggling.

See https://issues.civicrm.org/jira/browse/CRM-12300?focusedCommentId=72200&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-72200

Would be good to get this into 4.4.x LTS.