std: Rebuild sync::deque on Arc

This also removes the `&mut self` requirement, using the correct `&self`
requirement for concurrent types.
std: Rebuild mpmc queues on Unsafe/Arc

This removes usage of UnsafeArc and uses proper self mutability for concurrent
types.
std: Rebuild mpsc queue with Unsafe/&self

This removes the incorrect `&mut self` taken because it can alias among many
threads.
std: Rebuild spsc with Unsafe/&self

This removes the incorrect usage of `&mut self` in a concurrent setting.
std: Use Arc instead of UnsafeArc in BlockedTask
std: Build Exclusive on Arc<Unsafe<T>>

This removes the usage of UnsafeArc
std: Move comm primitives away from UnsafeArc

They currently still use `&mut self`, this migration was aimed towards moving
from UnsafeArc<T> to Arc<Unsafe<T>>
std: Remove UnsafeArc

This type has been superseded by Arc<Unsafe<T>>. The UnsafeArc type is a relic
of an era that has long since past, and with the introduction of liballoc the
standard library is able to use the Arc smart pointer. With little need left for
UnsafeArc, it was removed.

All existing code using UnsafeArc should either be reevaluated to whether it can
use only Arc, or it should transition to Arc<Unsafe<T>>

[breaking-change]
native: Remove UnsafeArc in favor of just Arc
rustuv: Remove usage of UnsafeArc
green: Remove usage of UnsafeArc
green: Remove some unsafe code in BasicLoop
std,green: Mark some queue types as NoShare
auto merge of #14301 : alexcrichton/rust/remove-unsafe-arc, r=brson

This type can be built with `Arc<Unsafe<T>>` now that liballoc exists.