This patch removes the hardcoded `distro_python_version`
mapping and usage from the configuration and templates,
aligning with the dynamic Python version detection
introduced in the dependent patch below.

The changes simplify the kolla-ansible roles by using
general `python3` paths, ensuring compatibility across
distributions without requiring version-specific handling.

Template files for Horizon, Ironic, Skyline, and others
have been updated to reflect this,
improving maintainability and reducing complexity.

Depends-On: https://review.opendev.org/c/openstack/kolla/+/926744
Change-Id: I85431b058b4184d96600cf17aaf8de871a018d61