Clarify the behavior of cleanup_removed_rollouts

[guilhermeeric]

Problem

There is a rake called cleanup_removed_rollouts to remove from redis rollouts that aren't present anymore on rollouts.yml. The way it's described it's intended that this rake will also remove from redis features that are released_to_all if they're not on rollouts.yml, but this doesn't actually happens.

cleanup_removed_rollouts will only remove features from redis if they're not on rollouts.yml and if they're released to individual IDs.

The rake description should clarify that released_to_all features will remain on redis even if not on rollouts.yml anymore.