[BUGFIX] User settings: Removed call to deprecated method render()

Call of FlashMessage->render() was replaced with appropriate code when
* setup was saved
* temporary data was cleared
* Notice for activated changes
* password is updated
* selected language is not available

Resolves: #73581
Releases: master, 7.6
Change-Id: I68432729334eb905e3aae112d42ae45177a70809
Reviewed-on: https://review.typo3.org/46794


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>