I just recently switched to using the Document Map view but it's title paired with the now-redundant vertical scrollbar started kind of bothering me. I've been using AutoHotKey for years and it usually works like a charm for dirty quick "hacks" such as this. After a little research I achieved the desired effect. Here's what I added to my script:

#IfWinExist ahk_class Notepad++
Control, Hide,,Button3, ahk_class Notepad++
ControlGet, Handle, Hwnd,, Scintilla2, ahk_class Notepad++
SendMessage, 2280, 0, 0,, ahk_id %Handle% ;SCI_SETVSCROLLBAR=2280,hide=0,show=1
#IfWinExist

Here's a screenshot:

Must note that I rearely close N++, so whenever I open it, I just reload my script and the redundant elements are gone (until I close and open it again). However, the same routine can be binded to any hotkey/shortcut instead of running it once on script load – see AHK manual.

NOTE:

Works for Notepad++ v6.9.1. If this doesn't work for your version, use AutoIt3 Window Spy program that is installed along with AutoHotkey to find the correct ClassNN value for the control you're trying to hide.

For example, on older versions, you may need to change Button3 to Button4 and Scintilla2 to Scintilla3

Horizontal scrollbar can be hidden by enabling View > Wordwrap