The updater is long broken: #1832 and all other tree methods are distributed. So maintaining this updater might not be necessary.

If we want to restore its support, first thing needed to to is implementing a method for tree updaters to access a buffered node position for running prediction, like what's in the old code (check out linked issue above). Then we need to re-enable column splitting in DMatrix. Lastly we need to fix the distcol.

I'm not eliminating the possibility of spiting data by column in the future, just suggesting we remove the current distcol. From above note, restoring the support might be best done from scratch to fit the more important updaters like histogram based algorithms.

@RAMitchell @hcho3