remove old forum code

[mboehn]

the forums haven't been used or maintained for quite a while

tested quick on the dev-server, didn't seem to break anything

[mboehn]

For cleaning up after removing forums.
please double check these, I haven't tested them.

• delete from GO_logs where logModule='forum';
• drop table GO_forums;
• drop table GO_forumPosts;
• drop table GO_forumThreads;
• alter table GO_users drop column forumPosts;