Remove dead Packaging Guide link [skip ci]

Author: j9liu

Documentation/developer-setup.md

@@ -36,8 +36,8 @@ There are detailed instructions for setting up a Cesium for Unreal development e
 
 ## Deployment instructions
 
-- The [Packaging Guide](packaging-guide.md) describes how to create a package and use it in a local Unreal installation. This is similar to installing it from the Unreal Engine Marketplace, but allows testing non-release branches.
 - The [Release Process](release-process.md) describes the necessary steps to publish a new version of the plugin to the Unreal Marketplace.
+- To package the plugin, take a look at the scripts that do the packaging on [GitHub Actions](https://github.com/CesiumGS/cesium-unreal/blob/main/.github/workflows/build.yml).
 
 ## Run the tests
 
@@ -55,4 +55,4 @@ There are detailed instructions for setting up a Cesium for Unreal development e
 - Run `npm install`
 - Run `npm run doxygen`
 
-The reference documentation will be written to `Documentation/Reference`.
+The reference documentation will be written to `Documentation/Reference`.