Remove ISO 8601 spec link from qtdoc's external-resources file.
Remove ISO 8601 spec link from qtdoc's external-resources file.

It is being added to corelib's external-resources file instead. See:
https://codereview.qt-project.org/#change,31489

Change-Id: Ib736267404cccd6ea895f0ff8203006f5712c73c
Reviewed-by: Jerome Pasion <c10995d24f6b454503389e8d00d837aef038985d@nokia.com>
Reviewed-by: Casper van Donderen <808524cef5c654648bea2a2b954f3b3445ed083c@nokia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc