[webapi][xwalk-1326] Remove test suite of CSS Style Attribute

- The feature for CSS Style Attribute (http://www.w3.org/TR/2013/REC-css-style-attr-20131107/) has been dropped, so remove this test suite.
Merge pull request #1260 from haoxli/webapi/xwalk-1326

[webapi][xwalk-1326] Remove test suite of CSS Style Attribute