Manual changes required for library removals.

The original PR only deleted the `.java` classes but still kept the pom.xml files and the java-game-servers module. Created a manual commit to:
- Delete the `java-game-servers` module.
- Remove `com.google.cloud:google-cloud-game-servers-bom` from the `` block in gapic-libraries-bom/pom.xml.

_Originally posted by @mpeddada1 in https://github.com/googleapis/google-cloud-java/issues/9787#issuecomment-1714163758_

While this change was handled manually for java-game-servers, there may be more cases in the future where the removal APIs requires these manual changes by the team. There is an opportunity to automate this.