This code was already reverted in the zuul images, it doesn't
actually provide the value is claims to add and it breaks the
running under podman.
Revert "Dockerfile: add support for arbritary uid"
This reverts commit da2701e0b1.
Revert "Dockerfile: add user to shadow file too"
This reverts commit 747e957263.
Change-Id: Iff606c65c6a3223f13d963d90455fa895193cce8