Use a group() instead of a static_library()

Win8 builds are failing with an empty libvpx.lib

Revert "Touch BUILD.gn to trigger a dependency"
Keep the "public_configs"

R=dpranke@chromium.org
TBR=dpranke@chromium.org
BUG=534943

Review URL: https://codereview.chromium.org/1364033003 .
1 file changed