Since we allocate raw zone memory for its inputs right behind the Node
object anyway, drop the previously OOB-accessed 1-element array within
the Node and use address computation to get to the inputs storage.
Note that this saves one pointer per Node, except for Nodes with zero
inputs, where it uses 1*sizeof(Use) more memory than before.

Bug: v8:3770
Change-Id: I7f5965c6f1b49013eb7f5a447b685d47decaa8fb
Reviewed-on: https://chromium-review.googlesource.com/c/1436218Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59141}