Remove unnecessary release from Arc::try_unwrap
The thread that recovers the unique access to Arc inner value (e.g., drop
when ref-count strong reaches zero, successful try_unwrap), ensures that
other operations on Arc inner value happened before by synchronizing
with release operations performed when decrementing the reference counter.
When try_unwrap succeeds, the current thread recovers the unique access
to Arc inner value, so release is unnecessary.
r? @Amanieu
aef2ca6681