The compilation state is mostly isolate-independent by now. It's only
the counters that are taken from one Isolate and then used throughout
the livetime of the NativeModule. This should be fixed in another CL.
The Isolate itself is never used from the compilation state, thus
remove the pointer.

R=mstarzinger@chromium.org

Bug: v8:8050
Change-Id: Ia605840b81352ede2c84a848081a14e51760e8c8
Reviewed-on: https://chromium-review.googlesource.com/c/1451824
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59367}