Revert "new primitive: discard_new_inode()"

Revert "new primitive: discard_new_inode()"

BugLink: https://bugs.launchpad.net/bugs/1838982
This reverts commit a5b1d6edcceaccbad1f964641992f820794fdfae.

This change was only added as a pre-req for "ovl: set I_CREATING
on inode being created" which got reverted from 4.15 as it was
causing regressions.

Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Khaled Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>