Remove remaining references to spring-cloud-function-deployer

[DidierLoiseau]

Describe the bug
The spring-cloud-function-deployer module was disabled in f96cd52 and removed in 32444f1, and is thus no longer published (since 5.0.0-M2), however there are remaining references that cause confusion:

• The official documentation still recommends it, as per docs/modules/ROOT/pages/spring-cloud-function/deploying-a-packaged.adoc,
• spring-cloud-function-dependencies still manages its version,
• spring-cloud-function-samples still uses it and cannot be built,
• and the module is still commented out in the main pom.xml.