Remove all traces of g_string_cookie_val.

I removed a check for that cookie being set from print_source_link() since I assume the only reason was to make sure it wasn't a spider and the access check will ensure that as well.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2012 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9