Don't delete anything, just hide it. You can do a few tricks in Explorer to clean up the navigation pane:
1. From Tools menu -> Folder Options: General tab You can uncheck the option "Show all folders" so a lot of unnecessary folders get hidden.
2. In Folder Options: View tab: Check the option: Hide empty drives in the Computer folder.
3. Right-click the individual libraries (Documents, Pictures etc) and choose "Don't show in navigation pane" so only the parent "Libraries" item gets shown.
4. To completely hide special items like Libraries, Homegroup, Network, if you don't need them in the navigation pane, you can use a tool like Windows 7 Navigation Pane Customizer:
http://www.door2windows.com/windows-7-navigation-pane-customizer-show-hide-rename-items-in-windows-explorer-navigation-pane/