svm: remove useless wrapping para tag around XML note entity

reference/svm/book.xml

@@ -9,8 +9,8 @@
 
  <preface xml:id="intro.svm">
   &reftitle.intro;
+  &warn.experimental;
   <para>
-   &warn.experimental;
    LibSVM is an efficient solver for SVM classification and regression problems.
    The svm extension wraps this in a PHP interface for easy use in PHP scripts.
   </para>