Remove taint support

Venema's taint feature was apparently never publicised beyond the
php-dev mailing list, and now there is a PECL taint extension which is
incompatible with the interface assumed here.

Grep confirms that wfArrayMap() is not used in any extensions.

Change-Id: I17d8d302947443262474c608829c7c7504bef589
Merge "Remove taint support"