GitLab

The sid sysroot change seems to have stuck.  Now remove the stretch sysroot so
we don't have to maintain both of them.

R=thestig

Change-Id: I5ae295143a3ca2db70299ea0773fd316ff04ac48
Reviewed-on: https://chromium-review.googlesource.com/950310Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541023}