Drop last sample, not first

[calum-chamberlain]

What does this PR do?

As identified in #573 - the first sample is sometimes dropped and the starttime is not adjusted leading to one-sample-out errors. I don't know why that was left in and the tests pass if we drop the last sample instead.

Why was it initiated? Any relevant Issues?

#573

PR Checklist

• develop base branch selected?
• This PR is not directly related to an existing issue (which has no PR yet).
• All tests still pass.
• Any new features or fixed regressions are be covered via new tests.
• Any new or changed features have are fully documented.
• Significant changes have been added to CHANGES.md.
• First time contributors have added your name to CONTRIBUTORS.md.