[usecase][XWALK-3089] Update CSP test default-src_self

- Because the test is to check whether the CSP (default-src self)
  only allow local font source loaded, remove the test content
  without CSS style applied.
- This is more like a workaround rather than actual fixing.
- This closes #1479.

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 1, Fail 0, Blocked 0