Fix documentation of how to publish artifacts to Maven Central

The preparations for publishing to the Google Cloud Storage are not
needed anymore.

Change-Id: I306de581fb30fa2bcacfacdc9de29194a5d9793f
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Bash: Deploy plugin archetypes to Maven Central

  ./tools/plugin_archetype_deploy.sh

This script builds and deploys plugin archetypes to Maven Central.

Change-Id: I4fc8e80f0907c2f43cf5f348a0f334c1e86f8db8