Remove references to artifact.md, regenerate graph

Signed-off-by: Jon Johnson <[email protected]>

annotations.md

@@ -16,10 +16,8 @@ This property contains arbitrary metadata.
 
 ## Pre-Defined Annotation Keys
 
-This specification defines the following annotation keys, intended for but not limited to [image index](image-index.md), image [manifest](manifest.md), [artifact](artifact.md), and [descriptor](descriptor.md) authors.
+This specification defines the following annotation keys, intended for but not limited to [image index](image-index.md), image [manifest](manifest.md), and [descriptor](descriptor.md) authors.
 
-* **org.opencontainers.artifact.created** date and time on which the artifact was built, conforming to [RFC 3339][rfc3339].
-* **org.opencontainers.artifact.description**: human readable description for the artifact (string)
 * **org.opencontainers.image.created** date and time on which the image was built, conforming to [RFC 3339][rfc3339].
 * **org.opencontainers.image.authors** contact details of the people or organization responsible for the image (freeform string)
 * **org.opencontainers.image.url** URL to find more information on the image (string)