Remove GYP_DEFINE reference from binutils/download.py

It appears that this isn't being set anywhere in recipes, so this should
maybe be safe to remove?

Bug: 718157
Change-Id: Iec1934638ec6f1acaf5b1b96c1e8fdb129457c39
Reviewed-on: https://chromium-review.googlesource.com/c/1308912
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#604301}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: b16601dcfc66c1479bd9e287bd5bcd7b38d5b99d