chore(v2): cleanup old v2 content from v1 branch (kubeflow#1083)

Author: Tomcli

guides/kfp-rebase-guide.md

@@ -118,6 +118,7 @@ git apply --reject --whitespace=fix \
     --exclude=contrib/* \
     --exclude=proxy/* \
     --exclude=test/* \
+    --exclude=v2/* \
     --exclude=third_party/* \
     --exclude=OWNERS \
     --exclude=VERSION \