Ozone: Remove the caca platform from the tree

This Ozone platform is not built by default, is not handled by the try
bots, does not have the required dependencies installed in the sysroot
and does not have any unit test. It is also really only useful as a
demo so instead of maintaining it, we can just update the documentation
to explain how to build the latest revision where it is known to work.


Review-Url: https://codereview.chromium.org/2445323002
Cr-Commit-Position: refs/heads/master@{#427635}
16 files changed