Fix layout test effect-reference-hidpi.html.

Unify it with the GPU version of this test
(effect-reference-hidpi-hw.html), which has no filter region set.

TBR=fmalita@chromium.org
BUG=240845

Review URL: https://codereview.chromium.org/1643013002

Cr-Commit-Position: refs/heads/master@{#372190}
2 files changed