Remove lucene-libs from contrib module packaging

As of Solr 9.0, Lucene is treated almost like a regular dependency of Solr (some slight exceptions). However the contrib module packaging still separates dependency libraries into contribs/<contrib>/lib and contribs/<contrib>/lucene-libs. Now that Lucene can be treated as any other dependency, there should be no need to separate the contrib module dependencies into separate directories.

This will also make it easier for users to include contrib modules, since they won't have to check which ones require loading in 2 jar directories, and which only require 1.