Drop writing MM and sTGC DigitContainers to the RDO file

We have noticed that some variables in the persistent MM_Digits appear to be uninitialized (ATLASSIM-5665). This causes spurious failures in the digitization ART tests. The simplest solution is to drop these containers as the MM_RDOs are also written to the RDO file. Dropped sTGC Digits also. (These changes are only for legacy configuration, as this is already the case for CA-based configuration.)

NB This may require scheduling RDOtoDigit converters in the RDOtoRDOTrigger step. This should go in after !50608 (merged) has been merged. Tagging @rosati, @jojungge, @stavrop, @chchau