Update timeslice script

Remove unnecessary check for image filenames. This was for images
generated with LapseIt Pro and I'm no longer using that.
Update timeslice script

Create the first timeslice segment at offset 0. It was previously being
created at an offset of around 85 (based on a 2048 wide image).
Update timeslice script

Increase the width of the last segment so that the resulting timeslice
image is the same width as the source images.
Remove unnecessary comment
Remove unnecessary statement