Revert "[BUGFIX] Links on external pages don't get indexed"

This reverts commit 819b5be0ac81004371fee2f0e6386cc32233a59b

Discussion with Mario Rimann and Stefan Neufeind leads to the conclusion
that this patch breaks current behaviour and that it's not possible to
implement both use cases without an extra setting. Agreement was to
revert this change and turn the bug report into a feature request.

Change-Id: Iebb62c89959328cc460fea5f1f46fb824b892822
Reviewed-on: https://review.typo3.org/22552
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert