Update hazelcast-jet-spring-boot-starter to indicate no longer required

[Holmistr]

Report from Neil:

com.hazelcast.jet.contrib:hazelcast-jet-spring-boot-starter should be updated to confirm it is no longer required

This was a module that would assist with autowiring Hazelcast Jet for Spring Boot, as a JetInstance @Bean,
based on the presence of Jet classes on the classpath and a config file.

(I've tested with 5.0, you don't need it)