man: drop whitespace from final <programlisting> lines

In the troff output, this doesn't seem to make any difference. But in the
html output, the whitespace is sometimes preserved, creating an additional
gap before the following content. Drop it everywhere to avoid this.

man/systemd.exec.xml

@@ -4722,7 +4722,7 @@ OnFailure=myhandler.service
 
 [Service]
 ExecStart=/bin/myprogram
-        </programlisting>
+</programlisting>
 
         <para>A service <filename index="false">mysuccess.service</filename> which can trigger an
         <varname>OnSuccess=</varname> dependency.</para>
@@ -4734,7 +4734,7 @@ OnSuccess=myhandler.service
 
 [Service]
 ExecStart=/bin/mysecondprogram
-        </programlisting>
+</programlisting>
 
         <para>A service <filename index="false">myhandler.service</filename> which can be triggered
         by any of the above services.</para>
@@ -4745,7 +4745,7 @@ Description=Acts on service failing or succeeding
 
 [Service]
 ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"
-        </programlisting>
+</programlisting>
 
         <para>If <filename index="false">myfailer.service</filename> were to run and exit in failure,
         then <filename index="false">myhandler.service</filename> would be triggered and the
@@ -4757,7 +4757,7 @@ MONITOR_EXIT_CODE=exited
 MONITOR_EXIT_STATUS=1
 MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236
 MONITOR_UNIT=myfailer.service
-        </programlisting>
+</programlisting>
 
         <para>If <filename index="false">mysuccess.service</filename> were to run and exit in success,
         then <filename index="false">myhandler.service</filename> would be triggered and the
@@ -4769,7 +4769,7 @@ MONITOR_EXIT_CODE=exited
 MONITOR_EXIT_STATUS=0
 MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697
 MONITOR_UNIT=mysuccess.service
-        </programlisting>
+</programlisting>
 
     </example>