Remove unnecessary "Not safe to send CSV data" complaint from elog.c's fallback

Remove unnecessary "Not safe to send CSV data" complaint from elog.c's fallback
path when CSV logging is configured but not yet operational.  It's sufficient
to send the message to stderr, as we were already doing, and the "Not safe"
gripe has already confused at least two core members ...

Backpatch to 9.0, but not further --- doesn't seem appropriate to change
this behavior in stable branches.