remove predefined AI in some skirmish maps, so that the default is taken

git-svn-id: http://svn.wildfiregames.com/public/ps/trunk@15463 3db68df2-c116-0410-a063-a993310a9797
Petra: hopefully improve the gatherers management + some cleanings

git-svn-id: http://svn.wildfiregames.com/public/ps/trunk@15464 3db68df2-c116-0410-a063-a993310a9797
Petra: fix the fix preventing the AI to be stuck trying to produce unavailable units

git-svn-id: http://svn.wildfiregames.com/public/ps/trunk@15465 3db68df2-c116-0410-a063-a993310a9797
Merge 'remotes/trunk'