* process._getActiveHandles() returns a list containing all active handles
(timers, sockets, etc.) that have not been unref'd.
* process._getActiveRequests() returns a list of active requests (in-flight
actions like connecting to a remote host, writing data to a socket, etc.).
It was decided that the performance benefits that isolates offer (faster spin-up
times for worker processes, faster inter-worker communication, possibly a lower
memory footprint) are not actual bottlenecks for most people and do not outweigh
the potential stability issues and intrusive changes to the code base that
first-class support for isolates requires.
Hence, this commit backs out all isolates-related changes.
Good bye, isolates. We hardly knew ye.