tree-wide: replace obsolete wiki links with systemd.io/manpages

All wiki pages that contain a deprecation banner
pointing to systemd.io or manpages are updated to
point to their replacements directly.

Helpful command for identification of available links:
git grep freedesktop.org/wiki | \
    sed "s#.*\(https://www.freedesktop.org/wiki[^ $<'\\\")]*\)\(.*\)#\\1#" | \
    sort | uniq

test/fuzz/fuzz-unit-file/systemd-machined.service

@@ -11,7 +11,7 @@ service
 [Unit]
 Description=Virtual Machine and Container Registration Service
 Documentation=man:systemd-machined.service(8)
-Documentation=https://www.freedesktop.org/wiki/Software/systemd/machined
+Documentation=man:org.freedesktop.machine1(5)
 Wants=machine.slice
 After=machine.slice
 RequiresMountsFor=/var/lib/machines

test/fuzz/fuzz-unit-file/systemd-resolved.service

@@ -11,7 +11,7 @@ service
 [Unit]
 Description=Network Name Resolution
 Documentation=man:systemd-resolved.service(8)
-Documentation=https://www.freedesktop.org/wiki/Software/systemd/resolved
+Documentation=man:org.freedesktop.resolve1(5)
 Documentation=https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
 Documentation=https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
 DefaultDependencies=no