[webapi][XWALK-3212] Remove this w3c test including idlharness

- Remove w3c mediastreamtrack-init-manual.html, since this is idlharness test
Merge pull request #1531 from xinliux/webapi/gumallow/XWALK-3212

[webapi][XWALK-3212] Remove this w3c test including idlharness