tree-wide: drop spurious newlines (#8764)

Double newlines (i.e. one empty lines) are great to structure code. But
let's avoid triple newlines (i.e. two empty lines), quadruple newlines,
quintuple newlines, …, that's just spurious whitespace.

It's an easy way to drop 121 lines of code, and keeps the coding style
of our sources a bit tigther.

man/systemd.exec.xml

@@ -353,7 +353,6 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
     </variablelist>
   </refsect1>
 
-
   <refsect1>
     <title>Security</title>
 
@@ -746,7 +745,6 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
     </variablelist>
   </refsect1>
 
-
   <refsect1>
     <title>Sandboxing</title>
 
@@ -2637,5 +2635,4 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
       </para>
   </refsect1>
 
-
 </refentry>