Removing "soft" subtitles (where the subtitles are not part of the actual video stream) is a piece of cake when using MKVToolNix.  MKVToolNix is a set of tools to create, alter and inspect Matroska files under Linux, other Unices and Windows.

Download MKVToolNix

Launch the tool & load your video file.  The list of tracks, chapters and tags will be populated.  It's then a simple task of unchecking the subtitle(s) you want to remove.  Set the output filename, click "Start muxing" and in a few seconds you'll be finished.

Removing Subtitles from Matroska files