elog() was set up to call abort() if it saw an ERROR or FATAL exit

elog() was set up to call abort() if it saw an ERROR or FATAL exit
during InitProcessingMode and the CurrentTransactionState was neither
TRANS_DEFAULT nor TRANS_DISABLED.  Unfortunately, after someone's recent
change to start the transaction manager earlier in startup than it used
to be started, that caused an abort() and consequent database system
reset on quite harmless errors (such as rejecting an invalid user name!).
As far as I can see, the test on CurrentTransactionState was completely
useless anyway, so I've removed it.