gfs2: Rename GLF_VERIFY_EVICT to GLF_VERIFY_DELETE

Rename the GLF_VERIFY_EVICT flag to GLF_VERIFY_DELETE: that flag
indicates that we want to delete an inode / verify that it has been
deleted.

To match, rename gfs2_queue_verify_evict() to
gfs2_queue_verify_delete().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>