fix: examples/extension-internal-flush: don't refer to a standalone layer arn for internal extension deploy

Author: jlizen

examples/extension-internal-flush/README.md

@@ -20,11 +20,9 @@ without introducing an observable delay.
 ## Build & Deploy
 
 1. Install [cargo-lambda](https://github.com/cargo-lambda/cargo-lambda#installation)
-2. Build the extension with `cargo lambda build --release`
+2. Build the function with `cargo lambda build --release`
 3. Deploy the function to AWS Lambda with `cargo lambda deploy --iam-role YOUR_ROLE`
 
-The last command will give you an ARN for the extension layer that you can use in your functions.
-
 ## Build for ARM 64
 
-Build the extension with `cargo lambda build --release --arm64`
+Build the function with `cargo lambda build --release --arm64`