Fix mantis 3065 (clear RA data)

Clear red alert data when resetting campaign progress, changing
campaigns and switching pilots
In CSG read, move RA data clear from the read RA section to the data
reset function (i.e. clear if CSG is valid, not if section contains
data)

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@11007 387891d4-d844-0410-90c0-e4c51a9137d3