Fix suggested JVM Garbage Collection options for JDK 11

Currently, the JVM garbage collection options suggested  in nuxeo.conf for Java 9 and higher are:

#JAVA_OPTS=$JAVA_OPTS -Xlog:gc*:file=${nuxeo.log.dir}/gc.log -verbose:gc

In Java 11, the -verbose:gc option is logging to the console and should be removed.
Logging to a file is enough.