sched_ext: Remove cpu.weight / cpu.idle unimplemented warnings

sched_ext generates warnings when cpu.weight / cpu.idle are set to
non-default values if the BPF scheduler doesn't implement weight support.
These warnings don't provide much value while adding constant annoyance. A
BPF scheduler may not implement any particular behavior and there's nothing
particularly special about missing cgroup weight support. Drop the warnings.

Signed-off-by: Tejun Heo <tj@kernel.org>