media: Update "d3d11-video-decoder" flag owner

Use //media/OWNERS instead of videostack-eng.

Change-Id: I78b14cc17159383df9af51ce3c1ffc02008d770c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2352690Reviewed-by: Frank Liberato <liberato@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797354}

chrome/browser/flag-metadata.json

@@ -743,7 +743,7 @@
   },
   {
     "name": "d3d11-video-decoder",
-    "owners": [ "liberato", "tmathmeyer", "videostack-eng" ],
+    "owners": [ "liberato", "tmathmeyer", "//media/OWNERS" ],
     "expiry_milestone": 78
   },
   {