HighSierra issues resolved in 10.13.4, re-enable tests

Bot is already on 10.14, so doesn't make a big difference, but cleaning
up legacy exceptions.

Bug: 777457, 777590
Change-Id: I2bcfa48bd094272f38274d2d5c98d5a37e7f6f6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2021186
Commit-Queue: Eric Karl <ericrk@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Eric Karl <ericrk@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735193}

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

@@ -5,5 +5,3 @@
 # Accelerated 2D canvas is not available on Linux due to driver instability
 crbug.com/254724 [ linux ] HardwareAcceleratedFeature_canvas_accelerated [ Failure ]
 
-crbug.com/777590 [ highsierra nvidia ] HardwareAcceleratedFeature_canvas_accelerated [ Failure ]
-