Revert "Mark WebGL test gl-bindAttribLocation-matrix.html flaky"

This reverts commit 9f069147.

Reason for revert: failures were actually caused by colliding text expectations in Issue 905682

Original change's description:
> Mark WebGL test gl-bindAttribLocation-matrix.html flaky
> 
> TBR=kbr@chromium.org
> BUG=906092
> 
> Change-Id: I11105b926d35b5bcb16c2930c04f98db20e5f4b4
> Reviewed-on: https://chromium-review.googlesource.com/c/1340788
> Reviewed-by: Ella Ge <eirage@chromium.org>
> Commit-Queue: Ella Ge <eirage@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#608946}

TBR=kbr@chromium.org,eirage@chromium.org

Change-Id: I4b0ee2ab77581a1710626308d8bb9942dfe0a595
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 906092
Reviewed-on: https://chromium-review.googlesource.com/c/1341152Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609055}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -822,8 +822,6 @@ class WebGLConformanceExpectations(GpuTestExpectations):
         bug=610951)
     self.Fail('WebglExtension_EXT_sRGB',
         ['android', ('qualcomm', 'Adreno (TM) 418')], bug=610951)
-    self.Flaky('conformance/attribs/gl-bindAttribLocation-matrix.html',
-        ['android', ('qualcomm', 'Adreno (TM) 418')], bug=906092)
 
     # Nexus 6 (Adreno 420) and 6P (Adreno 430)
     self.Fail('conformance/context/' +