Remove duplicated WebGL layout tests.

third_party/WebKit/LayoutTests/fast/canvas/webgl/canvas-test-expected.txt

-This test ensures WebGL implementations interact correctly with the canvas tag.
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-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
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-Canvas.getContext
-PASS context exists
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-Checking canvas and WebGL interaction
-PASS canvas.width is 300
-PASS canvas.height is 150
-PASS pixels are 0,0,0,0
-PASS getViewport() is "0,0,300,150"
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-change display size of canvas and see that viewport does not change
-PASS getViewport() is "0,0,300,150"
-PASS canvas.width is 300
-PASS canvas.height is 150
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-change the actual size of the canvas and see that the viewport does not change
-PASS pixels are 64,128,192,255
-PASS gl.clearColor should not change after canvas resize
-PASS gl.colorMask should not change after canvas resize
-PASS getViewport() is "0,0,300,150"
-PASS pixels are 0,0,0,0
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-PASS successfullyParsed is true
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-TEST COMPLETE
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