Remove unused imports in jetty-gcloud

[janbartel]

jetty-10

There are old, unused test imports in the jetty-gcloud/jetty-gcloud-session-manager which should be removed:

    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-webapp</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty.websocket</groupId>
      <artifactId>websocket-servlet</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty.websocket</groupId>
      <artifactId>websocket-jetty-server</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty.toolchain</groupId>      <artifactId>jetty-test-helper</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.eclipse.jetty</groupId>
      <artifactId>jetty-slf4j-impl</artifactId>
      <scope>test</scope>
   </dependency>