* Skip non-increasing test with external memory when subsample is used.
* Increase bin numbers for boost from prediction test. This mitigates the effect of
non-deterministic partitioning.
* Generate column matrix from gHistIndex.
* Avoid synchronization with the sparse page once the cache is written.
* Cleanups: Remove member variables/functions, change the update routine to look like approx and gpu_hist.
* Remove pruner.
Instead of accessing data from the `original_page_`, access the data from the first page of the available batch.
fix#7476
Co-authored-by: jiamingy <jm.yuan@outlook.com>
