[TASK] Remove hardcoded TypoScript setup

TypoScript TemplateService contains some hard coded TS that is always
present. The two defaults config.extTarget and config.uniqueLinkVars
are now moved to EXT:frontend and registered with the usual API call.
styles.insertContent is removed since it was always hidden in the
object browser and probably never used by anyone.

Change-Id: I8d0fd7c91e0c3b7ac19bcf1e435bb911b597e525
Resolves: #42543
Related: #60567
Releases: 6.3
Reviewed-on: http://review.typo3.org/20279


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>