There does not appear to be any way to delete pages made with the standard Moodle 2 wiki module.

This issue has been reported here:

http://moodle.org/mod/forum/discuss.php?d=168875

At the moment, it seems that the only workaround is to access the Moodle database and delete pages and content there. This is not a viable solution for most Moodle users.

This coupled with MDL-27037 makes the Wiki module less and less usable.