Remove instruction to push run image to local registry

We pushed it in an earlier step

Signed-off-by: Natalie Arellano <[email protected]>

Author: Natalie Arellano

content/docs/extension-guide/create-extension/run-dockerfile-extend.md

@@ -28,16 +28,6 @@ cat $PWD/samples/extensions/cowsay/bin/generate
 
 The extension generates a `run.Dockerfile` that installs `cowsay` on the current run image.
 
-### Push run image to test registry
-
-Now that we are extending the run image (vs switching it, as in the previous example) it must reside in a registry
-so that we can pull its manifest (necessary for the extension process).
-
-<!-- test:exec -->
-```bash
-docker push localhost:5000/run-image-curl
-```
-
 ### Configure the `hello-extensions` buildpack to require `cowsay`
 
 Set the `BP_REQUIRES` build-time environment variable to configure the `hello-extensions` buildpack to require both `vim` and `curl` (review the `./bin/detect` script to see why this works).