Drop SingleCounterForRate #5185

What?

The SingleCounterForRate option was added to allow users to revert a breaking change in OpenTelemetry output concerning rate metric export. This option is temporary and will be removed in the release following its introduction.

Why?

To minimize user impact, we will allow users to revert to the previous exporting method for Rate metrics for one cycle. They can use the old method if it is mission critical for them.
However, we want to keep our set of options as clean as possible, so we'll remove the option after the first transitioning cycle.