Maybe: Remove Features from Scheduler

[alexandru]

We need to remove the [Features] field, as exposed by [Scheduler#features].

This field is meant to query for the features supported by the Scheduler, and currently scheduler implementations can support these features of interest:

1. “batching mode”, which executes TrampolinedRunnable instances one after another, on the same thread;
2. “tracing”, which signals that the underlying Scheduler is able to work with Local;

Unfortunately, this is a parametricity violation, aka an implementation leak, which is a bad practice in both OOP and FP.

We need to review the cases in which these feature flags are used, and maybe find a way to remove the need for them.