Remove glsl-construct-vec-mat-index flaky suppression on Windows.

conformance/glsl/constructors/glsl-construct-vec-mat-index.html is no
longer flaking according to the flakiness dashboard and FindIt.

Bug: 525188
Change-Id: Ic9668359a698589359077b2a52ac4c04c96bc5a1
Tbr: jmadill@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637433Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664912}

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

@@ -132,7 +132,6 @@ crbug.com/751849 [ win7 debug nvidia d3d11 passthrough ] conformance/extensions/
 crbug.com/angleproject/2103 [ win ] conformance/glsl/bugs/sampler-struct-function-arg.html [ Skip ]
 
 # Note that the following test seems to pass, but it may still be flaky.
-crbug.com/525188 [ win ] conformance/glsl/constructors/glsl-construct-vec-mat-index.html [ RetryOnFailure ]
 crbug.com/478572 [ win ] deqp/data/gles2/shaders/functions.html [ Failure ]
 crbug.com/931006 [ win ] conformance/textures/misc/texture-active-bind.html [ Failure ]
 crbug.com/951628 [ win no-passthrough ] conformance/rendering/blending.html [ Failure ]