deps: use latest shared config

[suztomo]

Stop declaring nexus-staging-maven-plugin because the plugin is
configured in the parent POM (shared config).

I confirmed this command works:

suztomo@suztomo2:~/cloud-sql-jdbc-socket-factory$ mvn clean deploy -V     -DaltDeploymentRepository=local::default::file:${local_staging_dir}     -DskipTests=true     -P=-release-sonatype     -P=-release-staging-repository     -P=-clirr-compatibility-check     -P=-checkstyle-tests     -P=-animal-sniffer 

[suztomo]

@hessjcg Can you review and merge this? This is needed to make a future release (go/cloud-java-ossrh-sunset).

[kgala2]

/gcbrun