Remove hardcoded WebAnimationsCSSIntegrationEnabled flag in DumpRenderTree

Many of the DRT animation tests are timeout. Due to Hardcoded setting of WebAnimationsCSSIntegrationEnabled is DumpRenderTree.

Note: WebAnimationsCSSIntegrationEnabled is by default false in WebPage and these are overrriden based on the HTML metadata i.e by adding "<!-- webkit-test-runner [ experimental:WebAnimationsCSSIntegrationEnabled=false ] -->" in the test content.