[Android] Fix that xwalk core library is missing resources

The script to generate xwalk core library is still trying
to fetch resources from xwalk core.
It should be xwalk core internal.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1978
Merge pull request #2117 from wang16/fix_core_internal

[Android] Fix that xwalk core library is missing resources