Cleanup upgrade code #1128
Description
While doing upgrade testing for #1111 I noticed the data version is not being bumped during upgrade. This needs to be fixed.
It is only possible to upgrade from 1.9 to 2.0 because 1.9 is the only older release that supports Hadoop 3. Accumulo 2 requires Hadoop 3. Currently the upgrade code has a lot of cruft that supports upgrading much older versions. Now is a good time to clean that up leaving only what is needed to upgrade from 1.9 to 2.0.