Refactor timeout handling to use timestamp only in channel/v2 handlers

[damiannolan]

Summary

The on the feat/ibc-eureka branch we're currently using the existing v1 type for Timeout which requires it to be fulfilled with both height AND timestamp before calling timeout.Elapsed.

This timeout construction is no longer needed in v2 handlers as we will rely on timeout timestamps only.
We can simply this code and not use the Timeout type, as well as removal any usage of heights in timeout handling.

This can be completed for all packet handlers in channel/v2.

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[AdityaSripal]

Also the timeout handling must use SECONDS instead of NANOSECONDS

[DimitrisJim]

done in #7464