dh-systemdはdebhelper 9.20160709で統合された

  * Apply patches from Michael Biebl to merge dh_systemd_enable
    and dh_systemd_start from the dh-systemd package.
    (Closes: #822670)
  * dh: Enable the systemd helpers by default in compat 10 and
    later.

ということは dh-systemd パッケージをbuild-dependsに含めなくてもいい。

• debian/compat が 10
• debian/control で Build-Depends: debhelper (>= 9.20160709)

が必要要件。

aptもこんな風にできるよな

diff -Nru apt-1.3~rc2/debian/changelog apt-1.3~rc2+nmu1/debian/changelog
--- apt-1.3~rc2/debian/changelog    2016-08-18 06:31:07.000000000 +0900
+++ apt-1.3~rc2+nmu1/debian/changelog   2016-08-25 11:42:41.000000000 +0900
@@ -1,3 +1,18 @@
+apt (1.3~rc2+nmu1) UNRELEASED; urgency=medium
+
+  * Non-maintainer upload.
+  * debian/compat
+    - set 10
+  * debian/control
+    - set Build-Depends: debhelper (>= 9.20160709) to enable merged
+      dh-systemd
+    - remove Builde-Depends: dh-systemd  
+  * debian/rules
+    - remove "--with systemd --parallel" for dh since it is enabled
+      by default now.
+
+ -- Hideki Yamane <[e-mail]>  Thu, 25 Aug 2016 11:42:41 +0900
+
 apt (1.3~rc2) unstable; urgency=medium

   [ Julian Andres Klode ]
diff -Nru apt-1.3~rc2/debian/compat apt-1.3~rc2+nmu1/debian/compat
--- apt-1.3~rc2/debian/compat   2016-08-18 06:31:07.000000000 +0900
+++ apt-1.3~rc2+nmu1/debian/compat  2016-08-25 11:41:12.000000000 +0900
@@ -1 +1 @@
-9
+10
diff -Nru apt-1.3~rc2/debian/control apt-1.3~rc2+nmu1/debian/control
--- apt-1.3~rc2/debian/control  2016-08-18 06:31:07.000000000 +0900
+++ apt-1.3~rc2+nmu1/debian/control 2016-08-25 11:41:40.000000000 +0900
@@ -6,11 +6,11 @@
  Julian Andres Klode <[e-mail]>,
  David Kalnischkies <[e-mail]>
 Standards-Version: 3.9.8
-Build-Depends: dpkg-dev (>= 1.17.14), debhelper (>= 9.20141010), libdb-dev,
+Build-Depends: dpkg-dev (>= 1.17.14), debhelper (>= 9.20160709), libdb-dev,
  gettext (>= 0.12), libcurl4-gnutls-dev (>= 7.19.4~),
  zlib1g-dev, libbz2-dev, liblzma-dev, liblz4-dev (>= 0.0~r126),
  xsltproc, docbook-xsl, docbook-xml, po4a (>= 0.34-2),
- cmake (>= 3.4), pkg-config, libgtest-dev <!nocheck>, dh-systemd
+ cmake (>= 3.4), pkg-config, libgtest-dev <!nocheck>
 Build-Depends-Indep: doxygen, w3m, graphviz
 Build-Conflicts: autoconf2.13, automake1.4
 Vcs-Git: https://anonscm.debian.org/git/apt/apt.git
diff -Nru apt-1.3~rc2/debian/rules apt-1.3~rc2+nmu1/debian/rules
--- apt-1.3~rc2/debian/rules    2016-08-18 06:31:07.000000000 +0900
+++ apt-1.3~rc2+nmu1/debian/rules   2016-08-25 11:41:55.000000000 +0900
@@ -11,7 +11,7 @@
 export CTEST_OUTPUT_ON_FAILURE=1

 %:
-   dh $@ --with systemd --parallel --buildsystem=cmake
+   dh $@ --buildsystem=cmake

 override_dh_install-indep:
    dh_movefiles

インストール先ディレクトリこれでいいの？

$ tree /etc/systemd/
/etc/systemd/
├── journald.conf
├── logind.conf
├── network
├── resolved.conf
├── system
│   ├── basic.target.wants
│   │   ├── snapper-cleanup.timer -> /lib/systemd/system/snapper-cleanup.timer
│   │   └── snapper-timeline.timer -> /lib/systemd/system/snapper-timeline.timer
(snip)
│   └── timers.target.wants
│       └── apt-daily.timer -> /lib/systemd/system/apt-daily.timer
├── system.conf
├── timesyncd.conf
├── user
└── user.conf

basic.target.wantsに入ってるけど、同じようなtimerのapt-daily.timerはtimers.target.wants以下に入ってる。このディレクトリは正しいのか？

あー

[Install]
WantedBy=basic.target

だから挙動は正しい。

中井さんのSystemd入門(1) - Unitの概念を理解するより

なお、serviceを有効化した際に、どのtargetの前提として設定するかは、そのserviceの設定ファイルの[Install]セクションにおいて、「WantedBy=」オプションで指定されています。

basic.targetが妥当なのか、timers.targetなのか、というとtimersのほうが妥当ではないか？
→やっぱりそう

It is recommended that timer units installed by applications get pulled in via Wants= dependencies from this unit. This is best configured via WantedBy=timers.target in the timer unit's "[Install]" section.