Bug 1585370 - Make NSIS a required component for builds r=dmajor

This reverts Bug 1355584 which made it optional for MinGW. We now use
it in MinGW so let's make it required again.

Differential Revision: https://phabricator.services.mozilla.com/D48883

--HG--
extra : moz-landing-system : lando

moz.configure

@@ -558,7 +558,7 @@ def makensis_progs(target):
 
     return tuple(candidates)
 
-nsis = check_prog('MAKENSISU', makensis_progs, allow_missing=True)
+nsis = check_prog('MAKENSISU', makensis_progs)
 
 # Make sure the version of makensis is up to date.
 @depends_if(nsis)