[webapi] Remove support.js in tct-xmlhttprequest-w3c-tests

Impacted tests(approved): new 0, update 8, delete 0
Unit test platform: [Android]
Unit test result summary: pass 214, fail 19, block 1

Comment: Fail to get correct value of "header.toLowerCase()"
when running "w3c/xmlhttprequest" on Android OS
Another, can we submit these Intel created tests to W3C web-platform-tests? If not, why we create them?

I think we shall remove all the test cases for the specifications that W3C web-platform-tests covers if we have no sufficient reason, for example, keep our copies for these tests that can be rewritten by `idlharness.js`.