Fix the android_webview build's gyp files after the changes in r22444.

The android_webview get's it's compiler flags from the Android build system,
so we should not be setting these flags in gyp when building the webview.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/399413002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22467 ce2b1a6d-e550-0410-aec6-3dcde31c8c00