man/systemd-dissect: various fixes

- Add synopsis to `--discover` and `--validate` options.
- `-l` is for `--list`, not for `--mtree`.

(cherry picked from commit a058222)
(edited to remove --validate for v253, where it doesn't exist)
(cherry picked from commit 44b29d9)

Author: aafeijoo-suse

man/systemd-dissect.xml

@@ -46,6 +46,9 @@
     <cmdsynopsis>
       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--copy-to</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg> <arg choice="opt"><replaceable>SOURCE</replaceable></arg> <arg choice="plain"><replaceable>PATH</replaceable></arg></command>
     </cmdsynopsis>
+    <cmdsynopsis>
+      <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--discover</option></command>
+    </cmdsynopsis>
   </refsynopsisdiv>
 
   <refsect1>
@@ -168,7 +171,6 @@
 
       <varlistentry>
         <term><option>--mtree</option></term>
-        <term><option>-l</option></term>
 
         <listitem><para>Generates a BSD
         <citerefentry project='die-net'><refentrytitle>mtree</refentrytitle><manvolnum>8</manvolnum></citerefentry>