Remove redundant entry in SlowTests

Fixes lint warning:
SlowTests:487 Expectation 'virtual/gpu/fast/canvas/canvas-composite-text-alpha.html' is redundant with 'fast/canvas/canvas-composite-text-alpha.html' in line 488

TBR=yiyix@chromium.org

Bug: 1093836
Change-Id: I041f5856a658527e70bb1c334c6dca651b090f99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2260425Reviewed-by: Chris Sharp <csharp@chromium.org>
Commit-Queue: Chris Sharp <csharp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781368}

third_party/blink/web_tests/SlowTests

@@ -484,7 +484,6 @@ crbug.com/980804 fast/scrolling/scrollbars/mouse-autoscrolling-on-scrollbar.html
 
 crbug.com/983642 virtual/gpu/fast/canvas/canvas-composite-alpha.html [ Slow ]
 crbug.com/983642 [ Mac Debug ] fast/canvas/canvas-composite-alpha.html [ Slow ]
-crbug.com/983642 virtual/gpu/fast/canvas/canvas-composite-text-alpha.html [ Slow ]
 crbug.com/983642 fast/canvas/canvas-composite-text-alpha.html [ Slow ]
 crbug.com/983642 virtual/gpu/fast/canvas/color-space/canvas-createImageBitmap-e_srgb.html [ Slow ]
 crbug.com/983642 [ Mac ] fast/canvas/color-space/canvas-createImageBitmap-e_srgb.html [ Slow ]