test: update our branched weakref to v8 3.24
deps: update v8 to 3.24.35.17
headers: remove env.h from node_internals.h

`env.h` is an internal header file and should not be copied or exposed
to the users.

Additionally, export convenience `Throw*` methods with `v8::Isolate*` as
a first argument.
pipe_wrap: use Instantiate() method

Retrieve a new client object via PipeWrap::Instantiate(). This method
performs appropriate checks to make sure everything is as it should be.