The safest and probably easiest way to remove it would be to:
- Follow dsi.cfw.guide all the way through installing Unlaunch*
- Set up melonDS on your computer
- Use the NAND backup dsi.cfw.guide has you make and the BIOS files from its dumper (run the dumper linked under DSi Emulation from Unlaunch directly)
- In melonDS, you set those by going to Config -> Emu settings, then select the files from the "DSi-mode" tab
- "DSi firmware" is not needed
- Open melonDS and go to System -> Manage DSi titles, then you should be able to delete it from there
- Now simply follow dsi.cfw.guide's Restoring NAND page to restore your backup with the title removed (this will also uninstall Unlaunch as the backup was made before installing it)
- You should be fine to skip the no$gba set up and testing in no$gba since you're not doing anything super dangerous, but I would still recommend it just in case, that'll also let you confirm the title has been deleted
- You could check that it's working in melonDS instead (File -> Boot firmware), but it looks like you need more BIOS files for that
*if you have another DSi with Unlaunch you can dump the BIOS files using that one, in which case you only need to go through the "Dumping NAND" page, no need to install Unlauch
Alternatively, you could just move it to the far right of the DSi Menu and ignore it