Update sync commit performance documentation to be consistent with other

non-durable items, per Robert Haas.

doc/src/sgml/perform.sgml

@@ -1157,9 +1157,9 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
 
      <listitem>
       <para>
-       Turn off <xref linkend="guc-synchronous-commit">;  there might be no
+       Turn off <xref linkend="guc-synchronous-commit">;  there is no
        need to write the <acronym>WAL</acronym> to disk on every
-       commit.  This can cause transaction loss after a server crash.
+       commit.
       </para>
      </listitem>
     </itemizedlist>