This reverts commit 9c01d875f3.

This is very confusing and messy.. but it's documented.
`ansible_become_*` variables actually take priority and override all `become_*`
variables set at the task level.

As such, using `ansible_become=true ansible_become_user=root` in
`inventory/hosts` causes issues because tasks that specify
`become: OTHER_USER` will be forced to run as `root` due to
`ansible_become_user`.

For some of these, the `ansible_` prefix does not seem to be needed,
but it's the canonical way to do things and it may become required in
newer Ansible versions.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3237

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/570

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/641

Putting a lot of comments inbetween `[matrix-servers]` and the example
host line may make someone decide to clean up the comment
and accidentally skip-over the `[matrix-servers]` part.