[CLEANUP] Unification of function naming

The usage of getBackendUser and getBackendUserAuthentication is mixed
up in the core. But at least in inheritance this should be consistent.

Rename ScheduleModuleController::getBackendUserAuthentication to
ScheduleModuleController::getBackendUser

Change-Id: Icf21b4565ed66d3dabaf1df2d62d6b022c07248c
Resolves: #64982
Releases: master
Reviewed-on: http://review.typo3.org/36823


Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>