tmpfiles: move offline-passwd.[ch] to src/tmpfiles

offline-passwd.[ch] are only used by systemd-tmpfiles and the relevant
test. And are not included in libshared. So, it is not suitable to
located under src/shared.

src/test/meson.build

@@ -290,12 +290,6 @@ tests += [
          [],
          '', 'timeout=120'],
 
-        [['src/test/test-offline-passwd.c',
-          'src/shared/offline-passwd.c',
-          'src/shared/offline-passwd.h'],
-         [],
-         []],
-
         [['src/test/test-escape.c'],
          [],
          []],

src/tmpfiles/meson.build

@@ -1,7 +1,14 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
-systemd_tmpfiles_sources = [
-        'src/tmpfiles/tmpfiles.c',
-        'src/shared/offline-passwd.c',
-        'src/shared/offline-passwd.h',
+systemd_tmpfiles_sources = files(
+        'tmpfiles.c',
+        'offline-passwd.c',
+        'offline-passwd.h')
+
+tests += [
+        [['src/tmpfiles/test-offline-passwd.c',
+          'src/tmpfiles/offline-passwd.c',
+          'src/tmpfiles/offline-passwd.h'],
+         [],
+         []],
 ]