Scheduler JNI throws exception when the major versions of JAR and libmesos don't match

In convert.cpp we compare the major versions of the native library and the jar. This makes upgrading frameworks unnecessarily hard because you would have to deploy Mesos and frameworks in lockstep.

Backwards-incompatible changes would warrant a major version bump but not
vise versa. Plus it's more standard to express and check dependency
versions outside of the code but through package metadata.

The proposed solution is to remove this major version check altogether.