This reverts commit 752de4406e.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3393

When running the playbook against an existing server, it invokes `register_new_matrix_user`
as part of the `matrix-user-creator` role, which runs before the
`systemd_service_manager`. At that time, `matrix-user-creator` detects
that Synapse is up (from before), but it's the old version. Services have not yet been
restarted, so it's actually the older Synapse version that is up, not
the new one. The old version does not support the `--exists-ok` flag yet.

Basically, this `--exists-ok` patch landed too early and has affected existing playbook
users that have an older version of Synapse in operation.

It will be safer to bring back this patch some time in the future.
However, users upgrading from Synapse <= v1.109.0 even long into the
future will bump into the same issue. As such, it would be better to
either add special handling or to delay bringing back this patch enough
so as to ensure everyone using the playbook is on Synapse >= 1.110.0.

Related to https://github.com/element-hq/synapse/pull/17304

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.