[WebGL] Remove suppression for shaderindexing/varying.html on Mac AMD

This test is no longer flaky.

TBR=kbr@chromium.org

Bug: chromium:928989
Change-Id: I61a0d0a97356a2f4a6d9ef8745fa4d9846063df6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042685Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739160}

content/test/gpu/gpu_tests/test_expectations/webgl2_conformance_expectations.txt

@@ -467,7 +467,6 @@ crbug.com/751254 [ mac amd ] deqp/functional/gles3/shaderindexing/mat_00.html [
 crbug.com/636648 [ mac amd ] deqp/functional/gles3/shaderindexing/mat_01.html [ RetryOnFailure ]
 crbug.com/644360 [ mac amd ] deqp/functional/gles3/shaderindexing/mat_02.html [ RetryOnFailure ]
 crbug.com/659871 [ mac amd ] deqp/functional/gles3/shaderindexing/tmp.html [ RetryOnFailure ]
-crbug.com/928989 [ mac amd ] deqp/functional/gles3/shaderindexing/varying.html [ RetryOnFailure ]
 
 # These seem to be provoking intermittent GPU process crashes on
 # the MacBook Pros with AMD GPUs.