Mark anago krel migration KEP as implemented

With the merge of the anago removal PR we can now consider that KEP as
done.

Signed-off-by: Sascha Grunert <[email protected]>

Author: saschagrunert

keps/sig-release/0000-anago-to-krel-migration/kep.yaml

@@ -7,4 +7,5 @@ reviewers:
 approvers:
   - "@justaugustus"
 creation-date: 2020-09-22
-status: implementable
+latest-milestone: v1.20
+status: implemented