Gradle plugins: update sonarqube and remove protobuf
Gradle plugins: update sonarqube and remove protobuf

Since https://jira.sonarsource.com/browse/SONARGRADL-30, we can now
safely update to sonarqube plugin v2.2.1.

The protobuf gradle plugin is now deprecated - instead of configuring
the new plugin supported by Google, this commits drops that part of the
gradle build since that proto->java conversion is rarely needed and can
be manually run by any member of the team.

spring-projects/spring-framework,spring-projects/spring-framework,spring-projects/spring-framework,spring-projects/spring-framework,spring-projects/spring-framework,spring-projects/spring-framework,spring-projects/spring-framework