Right-click on it and select Remove Folder

Sorry, I read toolbar instead of sidebar. The Other Bookmarks folder is a built-in default folder. I'm not sure if it can be removed without some code.

Yes, I mean the sidebar. It does not seem to make sense that its built in with no option to remove it. I don't have any use for it so it just sits there empty.

It's a default location for bookmarks to be saved for Users without losing them.

You can't remove or hide the Other Bookmarks folder in the sidebar as that list consists of treechildren that doesn't allow to select individual entries like possible in a regular menu drop-down list and also only allows limited styling via userChrome.css.