Cleanup Temporality Selector

[cijothomas]

Similar to https://github.com/open-telemetry/opentelemetry-rust/pull/2085, we should remove this trait/implementations from public API. The exporters can offer https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry-otlp/src/metric.rs#L172-L180 with_delta method to switch temporality to delta from the default cumulative. This reduces a lot of unnecessary code in metrics sdk without significantly losing any functionality. OTLP Exporter only allows 3 options : https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk_exporters/otlp.md

(We can ofcourse add with_lowmemory_temporality if needed)