stream: remove useage of _readableState/_writableState.highWaterMark
Replace with .readHWM or .writeHWM getters, part of #445 mega issue.
@nodejs/streams
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
stream, net, http