[BUGFIX] Remove ObjectMapper part from TS-Template

since porting ObjectMapper Configuration to ext_localconf.php
it is time to remove the same configuration from
ext_typoscript.setup.txt.

Resolves: #47212
Releases: 6.1, 6.0
Change-Id: I4f22f7ad3a82e96543e5476d88009a2d5a376bdd
Reviewed-on: https://review.typo3.org/19967
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
Reviewed-by: Benjamin Bretz
Tested-by: Benjamin Bretz
Reviewed-by: Markus Günther
Tested-by: Markus Günther
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf