Drop build dependency to NetworkManager-devel

The NetworkManager-devel package doesn't exist anymore and is provided
by NetworkManager-glib-devel. We already require NetworkManager-glib-devel when
needed, so the NetworkManager-devel dependency can be dropped.

NetworkManager-openvpn.spec

@@ -18,7 +18,6 @@ Source0:   https://download.gnome.org/sources/NetworkManager-openvpn/1.8/%{name}
 #Patch1: 0001-example.patch
 
 BuildRequires: gtk3-devel
-BuildRequires: NetworkManager-devel
 BuildRequires: NetworkManager-libnm-devel >= 1:1.2.0
 BuildRequires: glib2-devel
 BuildRequires: libtool intltool gettext