Changes

osmo-uecups-master: remove useradd

debian-bookworm-build already adds a user (as it is a combination of
debian-bullseye-build and debian-bullseye-jenkins, and the latter did
it). Remove the additional useradd in osmo-uecups-master to fix:

useradd: UID 1000 is not unique

I've looked through related configs and scripts and the username is not
hardcoded there.

Related: OS#6057
Change-Id: I28f2a110167f550e1b38332ed4e7124b9e76f312