Revert "(namespace) quota: Ensure qids map to the filesystem"

Revert "(namespace) quota: Ensure qids map to the filesystem"

BugLink: https://bugs.launchpad.net/bugs/1644165
This reverts commit ec41f5ac648ff7bd3ae671d67483b5290bff68e6.

The kernel fix for bug #1634964 breaks LXD userspace, in particular the
following commits:

ac7f3f73cb39 (namespace) vfs: Don't modify inodes with a uid or gid unknown to the vfs
ca52383ad6a6 (namespace) vfs: Don't create inodes with a uid or gid unknown to the vfs

LXD 2.0.6 will include changes to support these kernel changes, but it isn't
available yet on xenial, so for now we just revert these commits.

Signed-off-by: Luis Henriques <luis.henriques@canonical.com>