Revision 354046 added res_corosync as a replacement for res_ais, but didn't

actually remove res_ais. This commit removes it.

In addition, the 'install_prereq' script has been updated to no longer install
AIS dependency packages, and instead install Corosync packages instead.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@354459 65c4cc65-6c06-0410-ace0-fbb531ad65f3