Revert "templates: Reinstate unused version comparison functions with warning"

Revert "templates: Reinstate unused version comparison functions with warning"

We reinstated these functions before the 2.12 release with a warning
such that users upgrading to 2.12 who had custom scripts using them
would not get broken in the upgrade and agreed to remove them after
the 2.12 release. This removes them accordingly.

This reverts commit e7a831963 (templates: Reinstate unused version
comparison functions with warning).

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>