Revert "enable libaom"

This reverts commit 80428a9.

AV1 is not ready for the beta channel. Disable it on the M65 branch.

BUG=804400

Change-Id: I202d23e7ef4a495f9e65d9891fc605265fc90eb5
Reviewed-on: https://chromium-review.googlesource.com/878922
Reviewed-by: Dale Curtis <[email protected]>
Cr-Commit-Position: refs/branch-heads/3325@{#31}
Cr-Branched-From: bc084a8-refs/heads/master@{#530369}

DEPS

@@ -55,7 +55,7 @@ vars = {
   'checkout_telemetry_dependencies': False,
 
   # libaom provides support for AV1 but the bitstream is not frozen.
-  'checkout_libaom': True,
+  'checkout_libaom': False,
 
   # By default do not check out the Oculus SDK. Only available for Googlers.
   'checkout_oculus_sdk' : False,