To remove items from places sidebar in Nautilus, open the ~/.config/user-dirs.dirs file and remove lines that refer to items you don't want.
XDG_DESKTOP_DIR="$HOME/Desktop"
XDG_DOWNLOAD_DIR="$HOME/Downloads"
XDG_PUBLICSHARE_DIR="$HOME/Public"
XDG_DOCUMENTS_DIR="$HOME/Documents"
XDG_MUSIC_DIR="$HOME/Music"
XDG_VIDEOS_DIR="$HOME/Videos"
XDG_PICTURES_DIR="$HOME/Pictures"
To make these changes permanent, run the following command in your terminal:
echo "enabled=false" > ~/.config/user-dirs.conf