default features on tracing-subscriber

[Stormshield-robinc]

Hi,

I ran into a crash with a project using both tracing-subscriber and tracing-oslog.
The crash happens during the .init() of a subscriber.

I was able to backtrace the problem up to the feature "tracing-log" of tracing-subscriber.
With this feature, which is enabled by default, a log logger is silently created and initialized.
This causes a crash if an .init() is called later on.
(https://docs.rs/tracing-subscriber/latest/tracing_subscriber/util/trait.SubscriberInitExt.html#method.init)

The issue with tracing-oslog is that it does not deactivate the default features of tracing-subscriber, which include this "tracing-log".

Furthermore, I think it would be nice to restrict the features to only those used by your crate, in order to avoid unnecessary compilation.

If you are interested I can do the fix