cr_actions: nuke old ref blocks on a renameUnmerged
cr_actions: nuke old ref blocks on a renameUnmerged

These are all being replaced with new block IDs as part of the deep
copy anyway.

Issue: KBFS-723

keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client