You should be ok here. Older versions of Lectora have a “flash fallback” for videos. I can’t remember the exact version this occurred in but basically it checks if your browser is capable of playing HTML5 video first and if capable will play it in that first.
If it determines HTML5 video playback is not possible in the browser it will “fallback” to playing them in flash.
Hence the files you are seeing flashmediaelement.swf and player.swf these to my understanding allow the fallback to work.
Given flash is being depreciated L18 has a new option to publish to HTML5 only which would not include the fallback files.
So, as long as your users all have browsers capable of playing HTML5 video your older content will still work fine without you having to to anything; assuming you have no other flash files in your content like you stated.