remove Animations from chrome-devtools' user test shim (#26494)

It looks like it's successfully merging with the DOM definition now
instead.

tests/cases/user/chrome-devtools-frontend/definitions.js

@@ -1,6 +1,5 @@
 var Accessibility = {};
 var AccessibilityTestRunner = {};
-var Animation = {};
 var ApplicationTestRunner = {};
 var Audits = {};
 var Audits2 = {};