stream: remove Array.p.shift primordial from hotpath of RS.read()
Refs: https://github.com/nodejs/performance/issues/82
A small improvement noticed in performance of read():
confidence improvement accuracy (*) (**) (***)
webstreams/readable-async-iterator.js n=100000 0.75 % ±1.93% ±2.57% ±3.35%
webstreams/readable-read.js type='byob' n=100000 0.69 % ±1.21% ±1.61% ±2.10%
webstreams/readable-read.js type='normal' n=100000 *** 8.81 % ±1.55% ±2.07% ±2.70%