Now features are registered into a map of vectors, but
it looks like the vector is always 1-item long and is
used to keep pointer on feature, instead of the feature
itself.
Switch it into map of reference_wrapper-s.
Before this patch we could register more than one
feature under the same name, now we can't. But this
seems to be OK, as we don't actually do this. To catch
violations of this restriction there's an assert() in the
feature_service::register_feature.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
9b67226715