Modernise in-tree debian packaging

Update standards and dh compat versions, stop building the -dbg package
and build a dbgsym package instead.

debian/compat

@@ -1 +1 @@
-8
+11

debian/control

@@ -26,7 +26,7 @@ Build-Depends: debhelper (>= 8),
  libxml2-dev,
  meson (>= 0.41),
  valac (>=0.38)
-Standards-Version: 3.8.3
+Standards-Version: 4.1.4
 Homepage: https://wiki.gnome.org/Apps/Geary
 
 Package: geary
@@ -66,13 +66,3 @@ Description: Email application
  - Full-featured HTML and plain text message composer
  - Desktop notification of new mail
  - Compatible with GMail, Yahoo! Mail, Outlook.com and other IMAP servers
-
-Package: geary-dbg
-Architecture: any
-Section: debug
-Priority: extra
-Depends: geary (= ${binary:Version}), ${misc:Depends}
-Enhances: geary
-Description: Email client (debugging symbols)
- Geary is an mail application for GNOME. This package contains files
- required for producing useful stack traces when debugging Geary.

debian/rules

@@ -18,8 +18,9 @@ override_dh_auto_configure:
 override_dh_auto_build:
 	ninja -v -C debian/build
 
+# Remove this target altogether for 0.14
 override_dh_strip:
-	dh_strip --dbg-package=geary-dbg
+	dh_strip --dbgsym-migration='geary-dbg'
 
 override_dh_auto_install:
 	DESTDIR=${CURDIR}/debian/geary ninja -C debian/build install