replace reference/docker for github.com/distribution/reference v0.5.0

The reference/docker package was a fork of github.com/distribution/distribution,
which could not easily be used as a direct dependency, as it brought many other
dependencies with it.

The "reference' package has now moved to a separate repository, which means
we can replace the local fork, and use the upstream implementation again.

The new module was extracted from the distribution repository at commit:
b9b19409cf

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

remotes/docker/fetcher_fuzz.go

@@ -26,8 +26,6 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"strconv"
-
-	refDocker "github.com/containerd/containerd/reference/docker"
 )
 
 func FuzzFetcher(data []byte) int {
@@ -75,8 +73,3 @@ func FuzzFetcher(data []byte) int {
 	}
 	return 1
 }
-
-func FuzzParseDockerRef(data []byte) int {
-	_, _ = refDocker.ParseDockerRef(string(data))
-	return 1
-}