Remove "become" from baremetal-prep-virthost.yml

When running a playbook with become: true, it also runs the facts
module with sudo, so ansible_user_dir will have the value of the
root user, rather than the expected home directory of the
ansible_ssh_user.

Merge of patch[1] has uncovered this issue and below task is failing
during image build.
~~~
TASK [oooci-build-images : ironic-python-agent]
"Error when writing tar.tar archive at /root/ironic-python-agent.tar:
[Errno 13] Permission denied: '/root/ironic-python-agent.tar'"
~~~

Cause: During run of gather facts task in build-test-packages role -
ansible_user_dir fact got changed to "/root" because of become:true.

With this patch we are removing the not needed become:true.

[1] https://review.opendev.org/#/c/752681/

Related-Bug: 1895138
Change-Id: I7264cf9f3f91384b52bd91a1b57d9a23ff87d0b0

playbooks/baremetal-prep-virthost.yml

@@ -117,7 +117,6 @@
 - name: Run DLRN gate role and install repo
   hosts: undercloud
   gather_facts: true
-  become: true
   vars:
     artg_compressed_gating_repo: "/home/{{ undercloud_user }}/gating_repo.tar.gz"
     artg_repos_dir: "{{ repo_clone_dir|default('/opt/stack/new') }}"