README.md: update stale documentation
README.md: update stale documentation

Remove stale badges.

Change-Id: I934881eebac49fed39d39a7217bc784a926b7949
Reviewed-on: https://chromium-review.googlesource.com/1176132
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go