Silence rack-timeout INFO messages

These unstructured messages are quite noisy and don't provide much useful information in production:

source=rack-timeout id=RhEremul7w2 timeout=60000ms service=5ms state=completed
source=rack-timeout id=VMaWDTdCQo1 timeout=60000ms state=ready

https://github.com/sharpstone/rack-timeout/blob/master/doc/logging.md mentions:

Request state changes into timed_out and expired are logged at the ERROR level, most other things are logged as INFO. The active state is logged as DEBUG, every ~1s while the request is still active.

I think timeouts are worth logging, but everything else is not.

Relates to https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9123