chromium: Switch to use open-source PDF plugin.

The Chromium PDF plugin is now available as open source software and is
already included in the Chromium source tree in current stable, so there
is no need to extract it from the Chrome binary package anymore.

See release announcement at http://blog.foxitsoftware.com/?p=641

Signed-off-by: aszlig <aszlig@redmoonstudios.org>