Move card table clear before enqueuing pending references

The card table clearing in G1 (which is to clear card marks that the scan rs/update rs phase did for duplicate card detection) in the post evacuation phase is done between reference processing and reference enqueuing.

This prevents G1 to merge phase the latter into the former.

There is no reason to put card table clear there: both scan rs and update rs, which are the only phases that add regions to the list of regions to be cleared, already completely finished before.