Remove duplicate lines from srt files

For some reason the srt files have duplicate lines that seem to only appear after the WEBVTT marker lines:

WEBVTT
X-TIMESTAMP-MAP=MPEGTS:181083,LOCAL:00:00:00.000

The duplication also shows up on asciiwwdc.com (though in one case I didn't see it even though it was in the srt file, not sure why).

Cleanup script for reference:
https://gist.github.com/jawwad/244731e6cf0e831ffa77