ceph: do not clear I_COMPLETE from d_release

First, this was racy anyway: d_release isn't called until well after the
dentry is unhashed.  Second, this runs afoul of the recent dcache change
that clears d_parent prior to calling d_release (949854d0), causing a NULL
pointer dereference.

Signed-off-by: Sage Weil <sage@newdream.net>