Allow end time of lockup streams to be in the past

[smol-ninja]

^{Refer to discussion https://github.com/sablier-labs/v2-periphery/discussions/369 for historical context.}

Lockup Linear

Allow end time to be in the past by removing if (blockTimestamp >= timestamps.end) check.

Lockup Dynamic

Allow the timestamp of the last segment to be in the past by removing if (blockTimestamp >= currentSegmentTimestamp) check.

Lockup Tranched

Allow the timestamp of the last tranche to be in the past by removing if (blockTimestamp >= currentTrancheTimestamp) check.