MINOR: early data: Never remove the CO_FL_EARLY_DATA flag.

MINOR: early data: Never remove the CO_FL_EARLY_DATA flag.

It may be useful to keep the CO_FL_EARLY_DATA flag, so that we know early
data were used, so instead of doing this, only add the Early-data header,
and have the sample fetch ssl_fc_has_early return 1, if CO_FL_EARLY_DATA is
set, and if the handshake isn't done yet.