[TASK] Remove not used viewhelper in beuser

The SelectDefaultValueViewHelper in beuser is
not used at the moment and since TYPO3 fluid
6.1 it is possible to add a prependOption
with the default selectViewHelper.

Fixes: #45338
Releases: 6.1, 6.0

Change-Id: Ie47021c2d74441243d116cc6cfcbfbb8fd5fdb1e
Reviewed-on: https://review.typo3.org/18183
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn