distribution: Drop "Related GitHub Issues" section

These were added based on Stephen's recommendation [1].  But the new
distribution-API maintainers can port those pull-requests over after
the project is formed.  Or the docker/distribution maintainers can
land them before the new project is formed.  Either way, there's no
need to involve the TOB at this level of detail.

[1]: opencontainers#35 (comment)

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

proposals/distribution.md

@@ -59,8 +59,3 @@ The API spec is currently considered v2 and we will start the specification at v
 
 * Does this include the code of the docker-registry?
     * No. This is an API specification discussion.
-
-## Related GitHub Issues
-
-* Simplifies tag listing: docker/distribution#2169
-* Allows listing of manifests: docker/distribution#2199