Bump debhelper from old 10 to 12.

Changes-By: lintian-brush
Fixes: lintian: package-uses-old-debhelper-compat-version
See-also: https://lintian.debian.org/tags/package-uses-old-debhelper-compat-version.html

debian/compat

-10
+12

debian/control

@@ -2,7 +2,7 @@ Source: dovecot-exporter
 Section: admin
 Priority: optional
 Maintainer: Autistici/Inventati <debian@autistici.org>
-Build-Depends: debhelper (>= 10~), golang-any (>= 1.11), dh-golang
+Build-Depends: debhelper (>= 12~), golang-any (>= 1.11), dh-golang
 Standards-Version: 3.9.6
 
 Package: dovecot-exporter

debian/rules

@@ -5,7 +5,7 @@ export DH_GOLANG_EXCLUDES = vendor
 
 
 %:
-	dh $@ --with golang --with systemd --buildsystem golang
+	dh $@ --with golang --buildsystem golang
 
 override_dh_auto_install:
 	dh_auto_install