[M110][infra] Turn down unneeded platforms.

With M112 pushing to stable for Mac & Windows, they are no longer
required for extended stable on M110.

Change-Id: I12fe67a179f51f55628abe484f126ad43a4708ca
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4402022
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Reviewed-by: Gary Tong <gatong@chromium.org>
Cr-Commit-Position: refs/branch-heads/5481@{#1392}
Cr-Branched-From: 130f3e4-refs/heads/main@{#1084008}