Update debian compatibility and standards

- Update deprecated debian compatibility to 12
- Use debian-compat as build-depends following latest debian policy
- Update debian policy standard to 4.5.1
- fix lintian error superfluous-file-pattern in d/copyright

debian/control

@@ -2,11 +2,10 @@ Source: slick-greeter
 Section: x11
 Priority: optional
 Maintainer: Linux Mint <root@linuxmint.com>
-Standards-Version: 3.9.8
-Build-Depends: at-spi2-core,
+Standards-Version: 4.6.1
+Build-Depends: debhelper-compat (= 12),
+               at-spi2-core,
                dbus-x11,
-               debhelper (>= 9),
-               dh-autoreconf,
                gnome-common,
                fonts-ubuntu,
                libcanberra-dev,

debian/copyright

@@ -14,19 +14,11 @@ Copyright: 2012-2015 Rosetta Contributors and Canonical Ltd 2012
  2017 Clement Lefebvre <root@linuxmint.com>
 License: GPL-3
 
-Files: /usr/share/slick-greeter/badges/*
+Files: files/usr/share/slick-greeter/badges/*
 Copyright: 2013 zombifier
 License: CC-BY-3.0
 
-Files: /usr/share/slick-greeter/badges/mwm.png
-Copyright: 2012 Canonical Ltd
-           2013 Graham Inggs <graham@nerve.org.za>
-License: GPL-3
-Comment: Created in GIMP using /usr/share/unity-greeter/unknown_badge.png,
- from Ubuntu's unity-greeter package, as a template. As per:
- https://lists.ubuntu.com/archives/ubuntu-devel/2012-February/034800.html
-
-Files: /usr/share/slick-greeter/badges/budgie-desktop.png
+Files: files/usr/share/slick-greeter/badges/budgie-desktop.svg
 Copyright: 2017 David Mohammed <fossfreedom@ubuntu.com>
 License: CC-BY-3.0
 

debian/rules

@@ -3,7 +3,10 @@
 LDFLAGS+=-Wl,--as-needed
 
 %:
-	dh $@ --with autoreconf --fail-missing
+	dh $@ --with autoreconf
 
 override_dh_autoreconf:
 	NOCONFIGURE=1 dh_autoreconf ./autogen.sh
+
+override_dh_missing:
+	dh_missing --list-missing