Remove duplicated WebGL layout tests.

third_party/WebKit/LayoutTests/fast/canvas/webgl/index-validation-expected.txt

-CONSOLE WARNING: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
-Tests that index validation verifies the correct number of indices
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-On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
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-Testing with valid indices
-PASS gl.checkFramebufferStatus(gl.FRAMEBUFFER) is gl.FRAMEBUFFER_COMPLETE
-PASS getError was expected value: NO_ERROR : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-PASS getError was expected value: NO_ERROR : 
-Testing with out-of-range indices
-Enable vertices, valid
-PASS getError was expected value: NO_ERROR : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-PASS getError was expected value: NO_ERROR : 
-Enable normals, out-of-range
-PASS getError was expected value: NO_ERROR : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-PASS getError was expected value: INVALID_OPERATION : 
-Test with enabled attribute that does not belong to current program
-Enable an extra attribute with null
-PASS getError was expected value: NO_ERROR : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-PASS getError was expected value: INVALID_OPERATION : 
-Enable an extra attribute with insufficient data buffer
-PASS getError was expected value: NO_ERROR : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-Pass large negative index to vertexAttribPointer
-PASS getError was expected value: INVALID_VALUE : 
-PASS gl.drawElements(gl.TRIANGLES, 3, gl.UNSIGNED_SHORT, 0) is undefined.
-PASS successfullyParsed is true
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-TEST COMPLETE
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