Remove unset from documentation as it is no longer needed

[ci skip]

Author: probonopd

README.md

@@ -177,7 +177,6 @@ script:
   - make INSTALL_ROOT=appdir -j$(nproc) install ; find appdir/
   - wget -c -nv "https://github.com/probonopd/linuxdeployqt/releases/download/continuous/linuxdeployqt-continuous-x86_64.AppImage"
   - chmod a+x linuxdeployqt-continuous-x86_64.AppImage
-  - unset QTDIR; unset QT_PLUGIN_PATH ; unset LD_LIBRARY_PATH
   # export VERSION=... # linuxdeployqt uses this for naming the file
   - ./linuxdeployqt-continuous-x86_64.AppImage appdir/usr/share/applications/*.desktop -appimage