The read_io and write_io session statistics were added as part of WT-12653. But that change did not make the requisite changes to the server code for reading those statistics from WT. As a result, the server code asserts with these new statistics.

This ticket is to remove/revert those statistics to keep the build green.

Note that the statistics are a side part of WT-12653, which is really about better compression efficiency when WT is configured with small page sizes.