Shared Sections can be deleted/removed.
If you would no longer like a section to be shared with the rest of your pages, go back into the section properties on each page and un-click the 'shared section' box. This will mean that any new pages that you create will not have the shared section. However, it also means that any changes made to the shared section that you have kept will not be translated to the other pages that it is shared on.
If you would like to delete a shared section from all pages, you will need to manually go into each page that the section is shared on and un-click the 'shared section' box. Make sure you save your page each time you do this, otherwise it will re-share the section again.