feat: remove Spark connector module from this repo (#467)

The source code now lives in https://github.com/googleapis/java-pubsublite-spark

Author: jiangmichaellll

pom.xml

@@ -121,7 +121,6 @@
  <module>google-cloud-pubsublite</module>
  <module>grpc-google-cloud-pubsublite-v1</module>
  <module>proto-google-cloud-pubsublite-v1</module>
- <module>pubsublite-spark-sql-streaming</module>
  <module>pubsublite-beam-io</module>
  </modules>