These variables were being assigned in group_vars/matrix_servers to
values byte-identical (or functionally identical) to what the
respective role's defaults/main.yml already provides.

Beyond just being noise, such redundant overrides cause drift over
time. When a role's default is later updated to something saner or
better (for example, switched from a hardcoded value to a derivation
from another variable), the matching line in group_vars/matrix_servers
stays frozen at the old value and silently defeats the improvement,
because group_vars beats role defaults in Ansible's precedence order.

The maubot management hostname fix in
https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/5248
is an example of this: the role default had been improved to derive
from matrix_bot_maubot_hostname, but the stale group_vars override
held it back to matrix_server_fqn_matrix.

Removing these overrides lets the role defaults do their job.

Closes https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/5248

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>