Use dh_prep instead of deprecated “dh_clean -k”

debian/changelog

@@ -19,6 +19,7 @@ dpkg (1.16.1) UNRELEASED; urgency=low
   * Improve deb-split(5) format description by splitting debian-split
     member contents into a list.
   * Switch to debhelper compatibility level 7.
+    - Use dh_prep instead of deprecated “dh_clean -k”.
 
   [ Updated man page translations ]
   * German (Helge Kreutzmann).

debian/rules

@@ -75,7 +75,7 @@ endif
 install: check
 	dh_testdir
 	dh_testroot
-	dh_clean -k
+	dh_prep
 	dh_installdirs
 
 	cd build-tree && $(MAKE) DESTDIR="$(CURDIR)/debian/tmp" install