Revert "Allow tooltips to override the X and Y format"

This reverts commit 053d7f5f8f7e78712a1d5e1f0a54d75bf32f1e26.
Allow tooltips to override the X and Y format

We needed to display the values differently on the axis versus the
tooltip, so this preserves the default behavior, but allows the consumer
to override the format in the tooltip.