[DO NOT MERGE] Fix that code checkout via .DEPS.git will fail for crosswalk

Including two changes:
1. Remove "src" entry in .DEPS.git.
2. Add "ozone" to skip_child_include list. Because ozone also
   specify "src" in its custom_deps.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1894