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.time.xml

@@ -266,7 +266,7 @@ tomorrow Pacific/Auckland → Thu 2012-11-23 19:00:00
       yearly → *-01-01 00:00:00
    quarterly → *-01,04,07,10-01 00:00:00
 semiannually → *-01,07-01 00:00:00
-   </programlisting>
+</programlisting>
 
     <para>Examples for valid timestamps and their
     normalized form:</para>