With recent changes to 9P server, path walks are now safe inside
open, create, rename and setattr calls. To simplify the code, remove
the lazyopen=false mode that was used for bind mounts, and converge
all mounts to using lazy open.
PiperOrigin-RevId: 219508628
Change-Id: I073e7e1e2e9a9972d150eaf4cb29e553997a9b76