[TASK] FormEngine: Remove foreign_selector handling in ajax

The default values are now handled by DatabaseRowInitializeNew
provider and the following provider will then process the
field automatically. No need to set this anymore.

Resolves: #70594
Releases: master
Change-Id: I3554c2736275c283b525497c6f1f336d44b06549
Reviewed-on: http://review.typo3.org/43992


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>