Mesos Requires Maven to Use Java 7+

Previous check was invalid.   It is possible for java 8 to be installed without java 7 and the build will work (but this formula fails).  It is also possible for java 7 to be installed (passing this check), but mvn is configured to use java 6.   The correct check is to verify what java version mvn is using.
makes sense... we can remove it.   Does that mean sending a new PR?