dpkg: Mark for translation and unify "rm cleanup" string

Use an already existing string to avoid introducing a new string for
translation.

debian/changelog

@@ -4,6 +4,7 @@ dpkg (1.17.17) UNRELEASED; urgency=low
   * Add dpkg-vendor, Dpkg/File.pm and Dpkg/Util.pm to the list of files with
     translatable strings, so that they can be translated.
   * Fix some typos for versioned and mentioned in comments and changelogs.
+  * Mark for translation and unify "rm cleanup" string in dpkg.
 
   [ Updated programs translations ]
   * German (Sven Joachim).

src/help.c

@@ -393,7 +393,7 @@ void ensure_pathname_nonexisting(const char *pathname) {
   }
   debug(dbg_eachfile, "ensure_pathname_nonexisting running rm -rf '%s'",
         pathname);
-  subproc_reap(pid, "rm cleanup", 0);
+  subproc_reap(pid, _("rm command for cleanup"), 0);
 }
 
 void