No need to change the launcher icons

The KICAD_DESKTOP_FILE_ICON_PREFIX variable is empty by default and the KICAD_DESKTOP_FILE_ICON_KICAD variable is already set to 'kicad'.

See https://gitlab.com/kicad/code/kicad/-/commit/9ae44e39983d05a7cfba6dd07f2e414d8e05cf7d#652b665abdededa24d85a490d6d3aa23e98be77d_8_13