Remove unused ColumnarRowBlockPB
Remove unused ColumnarRowBlockPB

This PB isn't used anywhere. Rather than leaving it around to confuse people,
best to delete for now and add it back if we do a proper columnar scan
option on the wire.

Change-Id: I885670208731d84a90d8c42e9e2ea3bde57cce59
Reviewed-on: http://gerrit.ent.cloudera.com:8080/886
Reviewed-by: Matteo Bertozzi <1d5ca967930bde0bdce795acbf71a5e281d2d4e5@cloudera.com>
Tested-by: jenkins

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