Refactor: controller: Remove controller_option()

pcmkvalidate_cluster_options() already iterates over all the options,
validating them and adding their defaults to config_hash if the option
is missing or invalid. There's no need to call pcmkcluster_option(),
which iterates over everything in controller_options until it finds the
target, and then runs the same checks as before.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>