s4-dsdb: don't actually remove the sd_flags control, just mark it non-critical

s4-dsdb: don't actually remove the sd_flags control, just mark it non-critical

For controls that need to be seen by more than one module, it is best
to just mark them non-critical when handled, instead of removing
them. Otherwise lower modules can't see them.

In this case we want the operational module to see the SD_FLAGS
control